Multi-layer core golf ball

ABSTRACT

A golf ball comprising a core and a cover, wherein the core consists of: a solid inner core layer formed from a plasticized thermoplastic composition TP p  and having a diameter of 1.10 inch or less and a center Shore C hardness (H center ) of 50 or less, one or more optional intermediate core layers, and an outer core layer formed from at least one of a thermoset rubber composition and a thermoplastic composition TP and having a thickness of 0.200 inches or greater and an outer surface Shore C hardness (H outer surface ) of 70 or greater, wherein H outer surface &gt;H center , and H outer surface −H center ≧40. In another embodiment, the center Shore C hardness (H center ) is 40 or less, the outer surface Shore C hardness (H outer surface ) is 85 or greater, and H outer surface −H center ≧45. In one embodiment, an intermediate layer is disposed between the outer core layer and the cover.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation-in-part of the following: co-pending U.S. patent application Ser. No. 14/248,618, filed Apr. 9, 2014 (the '618 application”); co-pending U.S. patent application Ser. No. 14/248,487, filed Apr. 9, 2014 (the '487 application”); and co-pending U.S. patent application Ser. No. 14/460,416, filed Aug. 15, 2014 (the '416 application”). The '618 application is a continuation-in-part of U.S. patent application Ser. No. 14/248,487, filed Apr. 9, 2014, which is a continuation-in-part of U.S. patent application Ser. No. 13/958,854, filed Aug. 5, 2013, and also a continuation-in-part of U.S. patent application Ser. No. 14/035,074, filed Sep. 24, 2013. The '416 application is a continuation-in-part of U.S. patent application Ser. No. 14/145,578 filed Dec. 31, 2013, which is a continuation-in-part of U.S. patent application Ser. No. 13/323,128, filed Dec. 12, 2011, now U.S. Pat. No. 8,715,112, which is a divisional of U.S. patent application Ser. No. 12/423,921, filed Apr. 15, 2009, now U.S. Pat. No. 8,075,423. U.S. patent application Ser. No. 12/423,921 is a continuation-in-part of U.S. patent application Ser. No. 12/407,856, filed Mar. 20, 2009, now U.S. Pat. No. 7,708,656, which is a continuation-in-part of U.S. patent application Ser. No. 11/972,240, filed Jan. 10, 2008, now U.S. Pat. No. 7,722,482. U.S. patent application Ser. No. 12/423,921 is also a continuation-in-part of Ser. No. 12/407,865, filed Mar. 20, 2009, now U.S. Pat. No. 7,713,145, which is a continuation-in-part of U.S. patent application Ser. No. 11/972,240, filed Jan. 10, 2008, now U.S. Pat. No. 7,722,482. The entire disclosure of each of these related applications is hereby incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to multi-layer golf balls having a very high positive gradient core, including a very soft, low compression inner core layer formed from an unfoamed composition.

BACKGROUND OF THE INVENTION

U.S. Pat. No. 8,182,368 to Kamino et al. discloses a golf ball wherein the difference between the JIS-C hardness H4 of the core at its surface and the JIS-C hardness H3 of the core outer layer at its innermost portion is equal to or greater than 10.

U.S. Pat. No. 8,007,376 to Sullivan et al. discloses a golf ball having an inner core layer with a negative hardness gradient and an outer core layer with a positive hardness gradient.

U.S. Pat. No. 7,410,429 to Bulpett et al. discloses a golf ball wherein the hardness of the inner core outer surface is the same as or lower than the hardness of the geometric center and the hardness of the outer core layer outer surface is greater than the hardness of the inner surface.

U.S. Pat. No. 6,695,718 to Nesbitt discloses a golf ball including a center core component preferably formed from a sulfur-cured polybutadiene and a core layer component preferably formed from a peroxide-cured polybutadiene and a metal salt of a fatty acid.

Despite these, and additional disclosures of golf balls having various hardness gradient properties, there remains a need for a very high positive gradient core, including a very soft, low compression inner core layer formed from an unfoamed composition. Such core would provide good durability while also contributing to spin reduction.

SUMMARY OF THE INVENTION

A golf ball of the invention produces a desired spin profile of reduced spin off the driver meanwhile maintaining moderate spin off wedges and irons.

Inner Core Layer TPp Formed from a Plasticized Thermoplastic Composition, Outer Core Layer Formed from at Least One of a Thermoset Rubber Composition and a Thermoplastic Composition TP

In one embodiment, the invention is directed to a golf ball comprising a core and a cover. The core consists of an inner core layer, one or more optional intermediate core layers, and an outer core layer. The inner core layer is formed from a plasticized thermoplastic composition TP_(p), and has a diameter of 1.10 inch or less and a center Shore C hardness (H_(center)) of 50 or less. The outer core layer is formed from at least one of a thermoset rubber composition and a thermoplastic composition TP, and has a thickness of 0.200 inches or greater and an outer surface Shore C hardness (H_(outer surface)) of 70 or greater. The outer surface hardness of the outer core layer is at least 40 Shore C points greater than the center hardness of the inner core layer (that is, H_(outer surface)>H_(center), and H_(outer surface)−H_(center)≧40). In an alternative embodiment, the center Shore C hardness (H_(center)) is 40 or less, the outer surface Shore C hardness (H_(outer surface)) is 85 or greater, and outer surface hardness of the outer core layer is at least 45 Shore C points greater than the center hardness of the inner core layer (that is, H_(outer surface)>H_(center), and H_(outer surface)−H_(center)≧45).

The center Shore C hardness H_(center) is greater than 0 and up to 50. In one embodiment, H_(center) is from about 25 to 50.

The inner core layer may have a diameter of from about 0.10 inch to 1.10 inches. For example, the inner core layer may have a diameter of from about 0.10 inch to 1.0 inch, or from about 0.25 inch to 0.90 inch, or from about 0.45 inch to 0.85 inch.

The inner core layer may have an inner core outer surface Shore C hardness (H_(icos)) that differs from the center Shore C hardness H_(center) by up to about 5 Shore C. That is, in some embodiments, H_(center) is greater than H_(icos) by up to 5 Shore C, and in other embodiments, H_(center) is less than H_(icos) by up to about 5 Shore C. In still other embodiments, H_(center) and H_(icos) are substantially the same.

In one embodiment, the outer surface Shore C hardness H_(outer surface) is from 70 to about 95. In another embodiment H_(outer surface) may be greater than 75 and less than about 85. In still other embodiments, H_(outer surface) may be from about 75 to about 95.

The outer core layer has an outer core interface Shore C hardness (H_(outer core interface)), namely the extrapolated hardness from the curve produced by making hardness measurements on the cross-section of a core or ball radially outward from the center in about 2 mm increments as shown in FIG. 1. The interface hardness of a core layer is defined herein as the extrapolated hardness from the curve produced by making hardness measurements on the cross-section of a core or ball radially outward from the center in about 2 mm increments.

In one embodiment, the outer surface Shore C hardness H_(outer surface) is greater than an outer core layer interface Shore C hardness (H_(outer core interface)) by greater than 30. In another embodiment, the outer surface Shore C hardness H_(outer surface) is greater than the outer core layer interface Shore C hardness H_(outer core interface) by from 10 to 30. In yet another embodiment, the outer core layer interface Shore C hardness H_(outer surface) is greater than the outer core layer interface Shore C hardness H_(outer core interface) by less than 10.

The outer core layer has a thickness of at least 0.200 inch, and as great as about 0.780 inches, for example. In one embodiment, the outer core layer may have a thickness of greater than 0.250 inch and up to about 0.450 inches. In still another embodiment, the outer core layer may have a thickness of greater than 0.200 inch and up to about 0.350 inches.

In another embodiment, the outer surface Shore C hardness H_(outer surface)−the center Shore C hardness H_(center)≧about 45. In yet another embodiment, the outer surface Shore C hardness H_(outer surface)−the center Shore C hardness H_(center)≧about 50. In still another embodiment, the outer surface Shore C hardness H_(outer surface)−the center Shore C hardness H_(center)≧about 55. In an alternative embodiment, the outer surface Shore C hardness H_(outer surface)−the center Shore C hardness H_(center)≧from 40 to about 80. In one embodiment, the outer surface Shore C hardness H_(outer surface)−the center Shore C hardness H_(center)≧from 40 to about 70.

The inner core layer meanwhile has an inner core interface Shore C hardness (H_(inner core interface)). The inner core layer has a negative hardness gradient wherein the inner core interface Shore C hardness (H_(inner core interface)) is less than the center Shore C hardness, or a zero hardness gradient wherein the inner core interface Shore C hardness (H_(inner core interface)) is within 1 Shore C unit of the center Shore C hardness, or positive hardness gradient wherein inner core interface Shore C hardness (H_(inner core interface)) is greater than the center Shore C hardness.

The inner core layer may have an overall zero hardness gradient between center Shore C hardness (H_(center)) and interface Shore C hardness (H_(inner core interface)), wherein H_(inner core interface)=(H_(center)). Or, in another embodiment, −1<H_(inner core interface)−H_(center)<1. In yet another embodiment, the inner core layer may have a positive hardness gradient between center Shore C hardness (H_(center)) and interface Shore C hardness (H_(inner core interface)) wherein: 1<H _(inner core interface) −H _(center)<45, or 1<H _(inner core interface) −H _(center)<15, or 1<H _(inner core interface) −H _(center)<5.

For example, in one embodiment, 1<H_(inner core interface)−H_(center)≦5. In another embodiment, 2<H_(inner core interface)−H_(center)≦5. In yet another embodiment, 3<H_(inner core interface)−H_(center)≦5. In an alternative embodiment, 4<H_(inner core interface)−H_(center)≦5.

In other embodiments, the inner core layer may have an overall negative hardness gradient. For example, in one embodiment, −1>H_(inner core interface)−H_(center)≧−5.

In one embodiment, the outer core layer has an outer core interface Shore C hardness (H_(outer core interface)) such that the Shore C H_(outer core interface)−the Shore C H_(inner core interface)≦the Shore C H_(outer surface)−the Shore C H_(center). This occurs, for example, where: (i) the Shore C H_(inner core interface)>the Shore C H_(center), and the Shore C H_(outer core interface)=the Shore C H_(outer surface); (ii) the Shore C H_(inner core interface)=the Shore C H_(center), and the Shore C H_(outer core interface)<the Shore C H_(outer surface); (iii) the Shore C H_(inner core interface)>the Shore C H_(center), and the Shore C H_(outer core interface)<the Shore C H_(outer surface); and/or (iv) the Shore C H_(inner core interface)=the Shore C H_(center), and the Shore C H_(outer core interface)=the Shore C H_(outer surface).

A non-limiting example of (i) is where the Shore C H_(outer core interface) (88)−the Shore C H_(inner core interface) (47)≦the Shore C H_(outer surface) (88)−the Shore C H_(center) (42). In turn, an example of (ii) is where the Shore C H_(outer core interface) (83)−the Shore C H_(inner core interface) (42)≦the Shore C H_(outer surface) (88)−the Shore C H_(center) (42). And an example of (iii) is where the Shore C H_(outer core interface) (83)−the Shore C H_(inner core interface) (47)≦the Shore C H_(outer surface) (88)−the Shore C H_(center) (42). Finally, one example of (iv) is where the Shore C H_(outer core interface) (88)−the Shore C H_(inner core interface) (42)=the Shore C H_(outer surface)+(88)−the Shore C H_(center) (42).

In another embodiment, the outer core layer has an outer core interface Shore C hardness (H_(outer core interface)) such that the Shore C H_(outer core interface)−the Shore C H_(inner core interface)>the Shore C H_(outer surface)−the Shore C H_(center). This occurs, for example, where: (v) the Shore C H_(inner core interface)<the Shore C H_(center), and the Shore C H_(outer core interface)=the Shore C H_(outer surface); (vi) the Shore C H_(inner core interface)=the Shore C H_(center), and the Shore C H_(outer core interface)>the Shore C H_(outer surface); or (vii) the Shore C H_(inner core interface)<the Shore C H_(center), and the Shore C H_(outer core interface)>the Shore C H_(outer surface).

A non-limiting example of (v) is where the Shore C H_(outer core interface) (88)−the Shore C H_(inner core interface) (37 Shore C)>the Shore C H_(outer surface) (88)−the Shore C H_(center) (42). In turn, an example of (vi) is where the Shore C H_(outer core interface) (93)−the Shore C H_(inner core interface) (42)>the Shore C H_(outer surface) (88)−the Shore C H_(center) (42). And an example of (vii) is where the Shore C H_(outer core interface) (93)−the Shore C H_(inner core interface) (37)>the Shore C H_(outer surface) (88)−the Shore C H_(center) (42).

The plasticized thermoplastic composition TP_(p) may comprise: a) an acid copolymer of ethylene and an α,β-unsaturated carboxylic acid, optionally including a softening monomer selected from the group consisting of alkyl acrylates; methacrylates; fatty acids; and fatty acid salts; b) a plasticizer; and c) a cation source present in an amount sufficient to neutralize from about 0 to about 100% of all acid groups present in the composition. In one embodiment, the thermoplastic composition TP_(p) further comprises a non-acid polymer selected from the group consisting of polyolefins, polyamides, polyesters, polyethers, polyurethanes, metallocene-catalyzed polymers, single-site catalyst polymerized polymers, ethylene propylene rubber, ethylene propylene diene rubber, styrenic block copolymer rubbers, alkyl acrylate rubbers, and functionalized derivatives thereof.

In a specific embodiment, the acid copolymer of ethylene and an α,β-unsaturated carboxylic acid does not include a softening monomer, and the acid is selected from acrylic acid and methacrylic acid and is present in the acid copolymer in an amount of from about 15 to about 30 weight %, based on the total weight of the acid copolymer. The non-acid polymer may, for example, be an alkyl acrylate rubber selected from ethylene-alkyl acrylates and ethylene-alkyl methacrylates and present in an amount of greater than 50 wt. %, based on the combined weight of the acid copolymer and the non-acid polymer. The non-acid polymer may be ethylene-n-butyl acrylate, wherein the n-butyl-acrylate is present in an amount of 20 wt. % or greater, based on the total weight of the non-acid polymer composition.

Meanwhile, the outer core layer may comprise at least one of natural rubber, polybutadiene, polyisoprene, ethylene propylene rubber (EPR), ethylene-propylene-diene rubber (EPDM), styrene-butadiene rubber, butyl rubber, halobutyl rubber, polyurethane, polyurea, acrylonitrile butadiene rubber, polychloroprene, alkyl acrylate rubber, chlorinated isoprene rubber, acrylonitrile chlorinated isoprene rubber, polyalkenamer, phenol formaldehyde, melamine formaldehyde, polyepoxide, polysiloxane, polyester, alkyd, polyisocyanurate, polycyanurate, polyacrylate, and combinations thereof.

The outer core layer may alternatively or additionally comprise at least one of ionomers; highly neutralized ionomers; non-ionomeric acid polymers; polyurethanes, polyureas, and polyurethane-polyurea hybrids; polyester-based thermoplastic elastomers; polyamides, copolymers of ionomer and polyamide, polyamide-ethers, and polyamide-esters; ethylene-based homopolymers and copolymers; propylene-based homopolymers and copolymers; triblock copolymers based on styrene and ethylene/butylene; derivatives thereof that are compatibilized with at least one grafted or copolymerized functional group; and combinations thereof. For example, in one embodiment, the ionomer may comprise a highly neutralized ionomer.

The intermediate core layer may comprise at least one of ionomers; highly neutralized ionomers; non-ionomeric acid polymers; polyurethanes, polyureas, and polyurethane-polyurea hybrids; polyester-based thermoplastic elastomers; polyamides, copolymers of ionomer and polyamide, polyamide-ethers, and polyamide-esters; ethylene-based homopolymers and copolymers; propylene-based homopolymers and copolymers; triblock copolymers based on styrene and ethylene/butylene; derivatives thereof that are compatibilized with at least one grafted or copolymerized functional group; and combinations thereof. For example, in one embodiment, the ionomer may comprise a highly neutralized ionomer.

The intermediate core layer may alternatively or additionally comprise at least one of natural rubber, polybutadiene, polyisoprene, ethylene propylene rubber (EPR), ethylene-propylene-diene rubber (EPDM), styrene-butadiene rubber, butyl rubber, halobutyl rubber, polyurethane, polyurea, acrylonitrile butadiene rubber, polychloroprene, alkyl acrylate rubber, chlorinated isoprene rubber, acrylonitrile chlorinated isoprene rubber, polyalkenamer, phenol formaldehyde, melamine formaldehyde, polyepoxide, polysiloxane, polyester, alkyd, polyisocyanurate, polycyanurate, polyacrylate, and combinations thereof.

FIG. 2 illustrates one embodiment of a golf ball of the invention wherein golf ball 2 comprises solid inner core layer 4 formed from a plasticized thermoplastic composition TP_(p) and having a diameter of 1.10 inch or less and a center Shore C hardness (H_(center)) of 15 or less; an intermediate core layer 6; an outer core layer 8 formed from at least one of a thermoset rubber composition and a thermoplastic composition TP and having a thickness of 0.40 inches or greater and an outer surface Shore C hardness (H_(outer surface)) of 70 or greater; and a cover 10 formed about the core.

In one embodiment, an intermediate layer may be disposed between the outer core layer and the cover.

Further and different constructions are as follows.

Inner Core Layer Formed from a Thermoplastic Composition, Outer Core Layer Formed from a Thermoset Composition; & Inner Core Layer Formed from a Thermoplastic Composition, Outer Core Layer Formed from Thermoplastic Composition Different than that of the Inner Core Layer

In one different construction, the invention is directed to a golf ball comprising a core and a cover. The core consists of an inner core layer, one or more optional intermediate core layers, and an outer core layer. The inner core layer is a solid layer formed from an unfoamed thermoplastic composition, and has a diameter of 1.10 inch or less and a center Shore C hardness (H_(center)) of 50 or less. The outer core layer is formed from a thermoset composition, has a thickness of 0.200 inches or greater, and an outer surface Shore C hardness (H_(outer surface)) of 70 or greater. The outer surface hardness of the outer core layer is at least 40 Shore C points greater than the center hardness of the inner core layer.

In a further differing construction, the invention is directed to a golf ball comprising a core and a cover. The core consists of an inner core layer, one or more optional intermediate core layers, and an outer core layer. The inner core layer is a solid layer formed from an unfoamed first thermoplastic composition TP₁, and has a diameter of 1.10 inch or less and a center Shore C hardness (H_(center)) of 50 or less. The outer core layer is formed from a second thermoplastic composition TP₂, has a thickness of 0.200 inches or greater, and an outer surface Shore C hardness (H_(outer surface)) of 70 or greater. The outer surface hardness of the outer core layer is at least 40 Shore C points greater than the center hardness of the inner core layer.

H_(center) may alternatively be 45 or less, or 40 or less, or less than 40, or 35 or less, or less than 35, or 30 or less, or less than 30, or 25 or less or less than 25, or 20 or less, or less than 20, or 15 or less, or less than 15, or 13 or less, or less than 13, or a Shore C hardness within a range having a lower limit of 5 or 10 and an upper limit of 15 or 25 or 30 or 35 or 40.

The inner core layer may alternatively have a diameter of less than 1.10 inches, or 1.00 inches or less, or less than 1.00 inches, or 0.90 inches or less, or less than 0.90 inches, or 0.80 inches or less, or less than 0.80 inches, or 0.75 inches or less, or less than 0.75 inches, or a diameter within a range having a lower limit of 0.10 or 0.15 or 0.20 or 0.25 or 0.30 or 0.35 or 0.40 or 0.45 or 0.50 or 0.55 inches and an upper limit of 0.60 or 0.65 or 0.70 or 0.75 or 0.80 or 0.85 or 0.90 or 0.95 or 1.00 or 1.05 or 1.10 inches.

The inner core layer has an inner core outer surface having a Shore C hardness (H_(icos)) that differs from H_(center) by up to 5 Shore C. In another embodiment, H_(icos) and H_(center) differ by up to about 5 Shore C. In one embodiment, H_(center) is greater than H_(icos) by up to 5 Shore C. In another embodiment, H_(center) is less than H_(icos) by up to 5 Shore C. In other embodiments, H_(center) is greater than H_(icos) by up to 4 Shore C, or by up to 3 Shore C, or by up to 2 Shore C, or by less than 2 Shore C. Alternatively, H_(center) may be less than H_(icos) by up to 4 Shore C, or by up to 3 Shore C, or by up to 2 Shore C, or by less than 2 Shore C. In one embodiment, H_(center) and H_(icos) are substantially the same.

H_(outer surface) may alternatively be 75 or greater, or 70 or greater, or greater than 70, or 75 or greater, or greater than 75, 80 or greater, or greater than 80, or 85 or greater, or greater than 85, or 87 or greater, or greater than 87, or 89 or greater, or greater than 89, or 90 or greater, or greater than 90, or 91 or greater, or greater than 91, or 92 or greater, or greater than 92, or a Shore C hardness within a range having a lower limit of 80 or 85 or 87 or 89 and an upper limit of 90 or 91 or 92 or 95.

In one embodiment, H_(outer surface) is greater than an outer core layer inner surface Shore C hardness (H_(inner surface)) by greater than 30. In another embodiment, H_(outer surface) is greater than H_(inner surface) by from 10 to 30. In yet another embodiment, H_(outer surface) is greater than H_(inner surface) by less than 10.

The outer core layer may alternatively have a thickness of greater than 0.10 inches, or 0.20 inches or greater, or greater than 0.20 inches, or 0.30 inches or greater, or greater than 0.30 inches, or 0.35 inches or greater, or greater than 0.35 inches, or 0.40 inches or greater, or greater than 0.40 inches, or 0.45 inches or greater, or greater than 0.45 inches, or a thickness within a range having a lower limit of 0.005 or 0.010 or 0.015 or 0.020 or 0.025 or 0.030 or 0.035 or 0.040 or 0.045 or 0.050 or 0.055 or 0.060 or 0.065 or 0.070 or 0.075 or 0.080 or 0.090 or 0.100 or 0.200 or 0.250 inches and an upper limit of 0.300 or 0.350 or 0.400 or 0.450 or 0.500 inches.

In another embodiment, H_(outer surface)−H_(center)≧45. In yet another embodiment, H_(outer surface)−H_(center)≧50. In still another embodiment, H_(outer surface)−H_(center)≧55. In an alternative embodiment, H_(outer surface)−H_(center)>55. In a different embodiment, H_(outer surface)−H_(center)≧60. In other embodiments, H_(outer surface)−H_(center)≧60, or H_(outer surface)−H_(center)≧65, or H_(outer surface)−H_(center)>65, or H_(outer surface)−H_(center)≧70, or H_(outer surface)−H_(center)≧70, or H_(outer surface)−H_(center)≧75, or H_(outer surface)−H_(center)≧75, or H_(outer surface)−H_(center)≧80, or H_(outer surface)−H_(center)≧80.

Additionally, the inner core layer has an inner core interface Shore C hardness (H_(inner core interface)). See, e.g., FIG. 1 and discussion below relating to FIG. 1.

The inner core layer has a negative hardness gradient wherein the interface Shore C hardness of the inner core layer is less than the center Shore C hardness, or a zero hardness gradient wherein the interface Shore C hardness of the inner core layer is within 1 Shore C unit of the center Shore C hardness, or positive hardness gradient wherein the interface Shore C hardness of the inner core layer is greater than the center Shore C hardness.

In a particular embodiment, the inner core layer has a center Shore C hardness (H_(center)) within a range having a lower limit of 1 or 5 or 10 and an upper limit of 15 or 25 or 30 or 35 or 40 and an interface Shore C hardness (H_(inner core interface)) within a range having a lower limit of 5 or 10 or 15 and an upper limit of 15 or 20 or 25 or 30 or 35 or 40 or 50, and has an overall zero hardness gradient wherein H_(inner core interface)=H_(center) or wherein −1<H_(inner core interface)−H_(center)<1; or a positive hardness gradient wherein: 1<H _(inner core interface) −H _(center)<45, or 1<H _(inner core interface) −H _(center)<15, or 1<H _(inner core interface) −H _(center)<5.

For example, in one embodiment, 1<H_(inner core interface)−H_(center)≦5. In another embodiment, 2<H_(inner core interface)−H_(center)≦5. In yet another embodiment, 3<H_(inner core interface)−H_(center)≦5. In an alternative embodiment, 4<H_(inner core interface)−H_(center)≦5.

In other embodiments, the inner core layer may have an overall negative hardness gradient. For example, in one embodiment, −1>H_(inner core interface)−H_(center)≧−5. In yet another embodiment, −2>H_(inner core interface)−H_(center)≧−5. In still another embodiment, −3>H_(inner core interface)−H_(center)≧−5. In a different embodiment, −4>H_(inner core interface)−H_(center)≧−5.

In one embodiment, the outer core layer has an outer core interface Shore C hardness (H_(outer core interface)) such that H_(outer core interface)−H_(inner core interface)≦H_(outer surface)−H_(center). This occurs, for example, where: (i) H_(inner core interface)>H_(center), and H_(outer core interface)=H_(outer surface); (ii) H_(inner core interface)=H_(center), and H_(outer core interface)<H_(outer surface); (iii) H_(inner core interface)>H_(center), and H_(outer core interface)<H_(outer surface); and/or (iv) H_(inner core interface)=H_(center), and H_(outer core interface)=H_(outer surface).

A non-limiting example of (i) is where H_(outer core interface) (85 Shore C)−H_(inner core interface) (50 Shore C)≦H_(outer surface) (85 Shore C)−H_(center) (45 Shore C). In turn, an example of (ii) is where H_(outer core interface) (80 Shore C)−H_(inner core interface) (50 Shore C)≦H_(outer surface) (85 Shore C)−H_(center) (50 Shore C). And an example of (iii) is where H_(outer core interface) (80 Shore C)−H_(inner core interface) (55 Shore C)≦H_(outer surface) (85 Shore C)−H_(center) (50 Shore C). Finally, one example of (iv) is where H_(outer core interface) (85 Shore C)−H_(inner core interface) (50 Shore C)=H_(outer surface) (85 Shore C)−H_(center) (50 Shore C).

In another embodiment, H_(outer core interface)−H_(inner core interface)>H_(outer surface)−H_(center). This occurs, for example, where: (v) H_(inner core interface)<H_(center), and H_(outer core interface)=H_(outer surface); (vi) H_(inner core interface)=H_(center), and H_(outer core interface)>H_(outer surface); or (vii) H_(inner core interface)<H_(center), and H_(outer core interface)>H_(outer surface).

A non-limiting example of (v) is where H_(outer core interface) (85 Shore C)−H_(inner core interface) (45 Shore C)>H_(outer surface) (85 Shore C)−H_(center) (50 Shore C). In turn, an example of (vi) is where H_(outer core interface) (85 Shore C)−H_(inner core interface) (50 Shore C)>H_(outer surface) (80 Shore C)−H_(center) (50 Shore C). And an example of (vii) is where H_(outer core interface) (85 Shore C)−H_(inner core interface) (45 Shore C)>H_(outer surface) (80 Shore C)−H_(center) (50 Shore C).

Non-limiting examples of suitable thermoplastic compositions include at least one of ionomers; non-ionomeric acid polymers; polyurethanes, polyureas, and polyurethane-polyurea hybrids; polyester-based thermoplastic elastomers; polyamides, copolymers of ionomer and polyamide, polyamide-ethers, and polyamide-esters; ethylene-based homopolymers and copolymers; propylene-based homopolymers and copolymers; triblock copolymers based on styrene and ethylene/butylene; derivatives thereof that are compatibilized with at least one grafted or copolymerized functional group; and combinations thereof.

In the construction incorporating TP₁ and TP₂, the thermoplastic compositions for the inner core layer and outer core layer may in one embodiment have the same classification—e.g. each being a primarily iomomeric material, or HNP. In a different embodiment, the thermoplastic compositions for the inner core layer and outer core layer may have different classifications—e.g., the inner core layer comprising a primarily iomomeric material, whereas the outer core layer comprises a stiff thermoplastic polyurethane material.

In the construction incorporating a thermoset outer core layer composition, suitable thermoset compositions include, for example, a rubber-based composition comprising at least one of natural rubber, polybutadiene, polyisoprene, ethylene propylene rubber (EPR), ethylene-propylene-diene rubber (EPDM), styrene-butadiene rubber, butyl rubber, halobutyl rubber, polyurethane, polyurea, acrylonitrile butadiene rubber, polychloroprene, alkyl acrylate rubber, chlorinated isoprene rubber, acrylonitrile chlorinated isoprene rubber, polyalkenamer, phenol formaldehyde, melamine formaldehyde, polyepoxide, polysiloxane, polyester, alkyd, polyisocyanurate, polycyanurate, polyacrylate, and combinations thereof.

Optional intermediate core layers are disposed between the inner core layer and outer core layer and have an individual layer thickness within a range having a lower limit of 0.005 or 0.010 or 0.015 or 0.020 or 0.025 or 0.030 or 0.035 or 0.040 or 0.045 inches and an upper limit of 0.050 or 0.055 or 0.060 or 0.065 or 0.070 or 0.075 or 0.080 or 0.090 or 0.100 or 0.150 or 0.200 or 0.250 or inches. In one non-limiting embodiment, the core includes an intermediate layer formed from a rubber composition. In another non-limiting embodiment, the core includes an intermediate layer formed from an HNP composition. A core intermediate layer may have a hardness in the range of from about 10 Shore C to about 90 Shore C.

The multilayer core has an overall diameter of 1.00 inch or greater, or 1.20 inches or greater, or 1.25 inches or greater, or 1.30 inches or greater, or 1.35 inches or greater, or 1.40 inches or greater, or 1.45 inches or greater, or 1.50 inches or greater, or 1.51 inches or greater, or 1.53 inches or greater, or 1.55 inches or greater, or an overall diameter within a range having a lower limit of 0.50 or 0.70 or 0.75 or 0.80 or 0.85 or 0.90 or 0.95 or 1.00 or 1.10 or 1.15 or 1.20 or 1.25 or 1.30 or 1.35 or 1.40 or 1.45 or 1.50 or 1.51 or 1.53 or 1.55 and an upper limit of 1.55 or 1.60 or 1.61 or 1.62 or 1.63 or 1.64 inches.

The inner core layer has a compression of 40 or less, or 30 or less, or 25 or less, or less than 25, or 20 or less, or less than 20, or 15 or less, or less than 15, or 10 or less, or less than 10, or 5 or less, or less than 5, or 0 or less, or less than 0. Meanwhile, the core has an overall compression of 50 or greater, or 60 or greater, or 65 or greater, or 70 or greater, or 80 or greater, or greater than 80, or 85 or greater, or greater than 85, or 90 or greater, or an overall compression within a range having a lower limit of 50 or 60 or 65 or 70 or 80 or 85 and an upper limit of 90 or 95 or 100 or 110.

The inner core layer has a coefficient of restitution (“COR”) at 125 ft/s of 0.780 or less, or 0.650 or less, or 0.600 or less, or 0.550 or less, and the multilayer core has an overall COR of 0.795 or greater, or 0.800 or greater, or 0.810 or greater, or 0.815 or greater, or 0.820 or greater.

Golf balls of the present invention typically have a COR of 0.700 or greater, preferably 0.750 or greater, and more preferably 0.780 or greater. Golf balls of the present invention typically have a compression of 40 or greater, or a compression within a range having a lower limit of 50 or 60 and an upper limit of 100 or 120.

In one embodiment, a golf ball of the invention incorporates an intermediate layer (or inner cover layer) between the core and the cover (or between the core and outer cover layer). In such an embodiment, the intermediate layer or inner cover layer, formed about the core, has a surface hardness of from about 50 Shore D to about 80 Shore D.

The finished golf ball has a compression that is greater than a compression of the inner core layer and outer core layer, combined. In one embodiment, the compression of the finished golf ball is greater than the compression of the inner core layer and outer core layer, combined, by at least 10%. In another embodiment, the compression of the finished golf ball is greater than the compression of the inner core layer and outer core layer, combined, by at least 15%. In yet another embodiment, the compression of the finished golf ball is greater than the compression of the inner core layer and outer core layer, combined, by at least 20%, or by at least 25%, or by at least 30%, or by at least 35%, or by at least 40%, or by at least 50%, or by at least 55%, or by about 60% or greater.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features that are characteristic of the present invention are set forth in the appended claims. However, the preferred embodiments of the invention, together with further objects and attendant advantages, are best understood by reference to the following detailed description in connection with the accompanying drawings in which:

FIG. 1 is a graph depicting core hardness as a function of distance from the center and further depicting extrapolated interfaces for the inner and outer core layers according to one embodiment of a golf ball of the invention.

FIG. 2 depicts a side view of a golf ball according to one embodiment of the invention as detailed herein.

DETAILED DESCRIPTION

Several embodiments of a golf ball of the invention incorporating an inner core layer formed from a thermoplastic composition and an outer core layer formed from a thermoset Composition are illustrated in prophetic golf balls Ex. 1, Ex. 2, Ex. 3, and Ex. 4 and compared with one conventional prophetic golf ball Comp. Ex. 1. In this regard, at least one core layer in each of golf balls Ex. 1, Ex. 2, Ex. 3, Ex. 4 and Comp. Ex. 1 includes at least one of the rubber-based formulas set forth in TABLE I as follows:

TABLE I THERMOSET CORE MATERIALS INGREDIENTS Core Core Core (Phr) Formulation 1 Formulation 2 formulation 3 Polybutadiene 100 100 100 Zinc Oxide 5 5 5 Zinc diacrylate 35 38 31 (ZDA) Perkadox ® BC¹ 0.5 0.5 * Trigonox ® 265² * * 1 Antioxidant * * 0.4 ZnPCTP 0.5 0.5 0.5 ¹Perkadox ® BC is an initiating agent (Dicumyl peroxide) available from Akzo Nobel. ²Trigonox ®265 is an initiating agent available from Akzo Nobel.

TABLE II below details the construction and certain properties for prophetic golf balls Ex. 1, Ex. 2, Ex. 3, Ex. 4 and Comp. Ex. 1:

TABLE II Golf Ball Construction EXAMPLES & Properties Ex. 1 Ex. 2 Ex. 3 Ex. 4 Comp. Ex. 1 Inner Core Pebax ® Kraton ® Estane  ® Elvax ® Core Material 2533 SA 01³ D1101 K⁴ T370A TPU⁵ 40W⁶ Formulation 3⁷ Inner Core 0.75 0.50 0.75 0.50 1.00 Diameter (in.) Center Hardness 47.6 29.2 36.4 12.5 71.0 (Shore C) Inner Core ≦40 ≦40 ≦40 ≦40 >40 Compression Outer Core Core Core Core Core Core Material Formulation Formulation Formulation Formulation Formulation 1⁷ 2⁷ 1 2 1 Outer Core 0.400 0.525 0.400 0.525 0.275 Thickness (in.) Outer Core Surf. 87.9 88.6 88.1 89.2 87.5 Hardness (Shore C) Dual Core 77 68 65 52 88 Compression Intermediate Surlyn ® Surlyn ® Surlyn ® Surlyn ® Surlyn ® Layer Material 7940/8940⁸ 7940/8940 7940/8940 7940/8940 7940/8940 Intermediate 0.035 0.035 0.035 0.035 0.035 Layer Thickness (in.) Intermediate 69.1 68.8 68.8 68.9 69.3 Layer Hardness (Shore D) Cover Material MDI⁹/ MDI/ MDI/ MDI/ MDI/ PTMEG¹⁰/ PTMEG/ PTMEG/ PTMEG/ PTMEG/ E-300¹¹ E-300 E-300 E-300 E-300 Cover Thickness 0.030 0.030 0.030 0.030 0.030 (in.) Cover Hardness 82.1 81.9 82.0 82.2 82.1 (Shore C) Ball 86 78 76 61 99 Compression ³Pebax ®2533 SA 01 is a thermoplastic elastomer formed from flexible polyether and rigid polyamide, available from ARKEMA (polyether amide). ⁴Kraton ®D1101 K is a linear triblock copolymer based on styrene and butadiene, with a styrene content of 31%, available from KRATON Polymers Group (styrene block copolymer). ⁵Estane ®T370 A is a thermoplastic polyurethane available from Lubrizol. ⁶Elvax ®40W is an ethylene vinyl acetate copolymer resin available from DuPont (EVA). ⁷Core Formulations 1, 2 & 3 are set forth in TABLE I above. ⁸Surlyn ®7940 (Li) and Surlyn ®8940 (Na), are medium acid, monovalent and medium flow ionomers. ⁹Methylene diphenyl diisocyanate. ¹⁰Polytetramethylene ether glycol. ¹¹Ethacure 300, dimethylthiotoluene diamine, sold by Albemarle.

As evident from TABLE I, core formulations 1, 2 & 3 differ from each other in at least one of the amount of peroxide, the amount of zinc diacrylate, and presence/absence of an antioxidant.

Referring to golf balls Ex. 1, Ex. 2, Ex. 3, and Ex. 4 of TABLE II, each incorporates a dual core comprising a very soft, low compression inner core layer surrounded by a hard higher compression thermoset outer core layer. Additionally, each inner core layer has a diameter of less than 1.10 inches, is formed from an unfoamed thermoplastic composition, and has a center Shore C hardness of 50 or less. Meanwhile, each outer core layer has a thickness of 0.200 inches or greater, is formed from a thermoset composition, and has an outer surface Shore C hardness of 80 or greater. Finally, in each of the dual cores of golf balls Ex. 1, Ex. 2, Ex. 3, and Ex. 4, the outer core layer has an outer surface hardness that is at least 40 Shore C points greater than the center hardness of the inner core layer.

Specifically referring to golf ball Ex. 1, the inner core layer has a diameter of 0.75 in., is formed from a polyether amide, and has a center Shore C hardness of 47.6. The outer core layer meanwhile has a thickness of 0.400 in., is formed from core formulation 1, and has an outer surface Shore C hardness of 87.9. The outer surface hardness of the outer core layer of golf ball Ex. 1 is therefore “at least 40 Shore C points greater than the center hardness of the inner core layer” (namely 40.3 Shore C points greater than the center hardness).

Golf ball Ex. 3's construction/composition is different than that golf ball Ex. 1 in that the inner core layer of Ex. 3 is formed from a thermoplastic polyurethane rather than a polyether amide. Several property differences may also be noted between golf balls Ex. 3 and Ex. 1, respectively: inner core layer center Shore C hardnesses (36.4 versus 47.6); outer core layer surface Shore C hardnesses (88.1 versus 87.9); dual core compressions (65 versus 77); intermediate layer Shore D hardnesses (68.8 versus 69.1); cover layer surface shore C hardness (82.0 versus 82.1); and golf ball compression (76 versus 86). Nevertheless, golf ball Ex. 3 has an outer core layer outer surface hardness that is greater than the center hardness of the inner core layer by 51.7 Shore C hardness points, which is well above “at least 40 Shore C points greater”.

In turn, golf ball Ex. 4's construction/composition is different than that of golf ball Ex. 2 in that the inner core layer of Ex. 4 is formed from an EVA rather than a styrene block copolymer. Several property differences may also be noted between golf balls Ex. 4 and Ex. 2, respectively: inner core layer center Shore C hardnesses (12.5 versus 29.2); outer core layer surface Shore C hardnesses (89.2 versus 88.6); dual core compressions (52 versus 68); intermediate layer Shore D hardnesses (68.9 versus 68.8); cover layer surface shore C hardness (82.2 versus 81.9); and golf ball compression (61 versus 78). Yet both golf balls Ex. 2 and Ex. 4 have a very high positive hardness gradient wherein the outer surface hardness of the outer core layer is at least 40 Shore C points greater than the center hardness of the inner core layer, namely by 59.4 and 76.7 Shore C hardness points, respectively.

Comparative golf ball Comp. Ex. 1, in contrast to golf balls Ex. 1, Ex. 2, Ex. 3, and Ex. 4, is formed from a conventional thermoset rubber-based composition having a center Shore C hardness well above 50 (namely 71). Additionally, Comp. Ex. 1 incorporates an outer core layer having an outer surface Shore C hardness that is not “at least 40 Shore C points greater than the center hardness of the inner core layer” but rather, well below that, namely only 16.5 Shore C points greater.

Accordingly, each of golf balls Ex. 1, Ex. 2, Ex. 3, and Ex. 4 incorporates a core having a steep positive Shore C hardness gradient progressing from a hard core outer surface to a very soft center, whereas the core of golf ball Comp. Ex. 1 has a center Shore C hardness above 50 and a much more shallow Shore C hardness gradient from outer surface to center and well below “at least 40”.

Several different constructions incorporating an inner core layer formed from a thermoplastic composition and an outer core layer formed from a thermoplastic composition different than that of the inner core composition are illustrated in prophetic golf balls Ex. 5, Ex. 6, Ex. 7, and Ex. 8 and compared with one conventional prophetic golf ball Comp. Ex. 2 herein below.

Prophetic inventive golf balls Ex. 5, Ex. 6, Ex. 7, Ex. 8 and comparative prophetic golf ball Comp. Ex. 2 each comprise a core, a cover, and an intermediate layer disposed between the core and the cover. Additionally, every core is a dual core comprising an inner core layer surrounded by an outer core layer.

The inner core layers of inventive prophetic golf balls Ex. 5, Ex. 6, Ex. 6, and Ex. 7 are each formed from a different thermoplastic material, namely Elvax®150 (ethylene-vinyl acetate copolymer (EVA)), Nucrel®9-1 (olefin-unsaturated carboxylic acid ester terpolymer), Kraton® D0243 B (styrene block copolymer), and Riteflex®425 (thermoplastic polyester elastomer), respectively. In turn, the outer core layers of golf balls Ex. 5, Ex. 6, Ex. 7, and Ex. 8 are also each formed from a different thermoplastic composition as formulated in TABLE III:

TABLE III OUTER CORE LAYER MATERIALS (TP₂) Ingredients Ex. 5 Ex. 6 Ex. 7 Ex. 8 (Phr) TP₂(1) TP₂(2) TP₂(3) TP₂(4) Primacor ® 5980I¹² 43 48 48 47 Fusabond ® N525¹³ 11 * 12 * Elvaloy ® AC 3427¹⁴ * * * 13 Kraton FG1924 G¹⁵ * 12 * * Ethyl Oleate 10 * * * Oleic Acid 36 40 40 40 Mg(OH)₂ 8.0   8.9 8.9   8.8 ¹²Primacor ® 5980I is an Ethylene/-Acrylic Acid Copolymer available from Dow Chemical Company. ¹³Fusabond ® N525 is an anhydride modified ethylene copolymer available from E. I. du Pont de Nemours and Company, Inc. ¹⁴Elvaloy ® AC 3427 is a copolymer of ethylene and butyl acrylate available from E. I. du Pont de Nemours and Company, Inc. ¹⁵Kraton FG1924 G is a linear triblock copolymer based on styrene and ethylene/butylene with a polystyrene content of 13% (Styrene block copolymer) available from Kraton Polymers.

Meanwhile, in comparative golf ball Comp. Ex. 2, both the inner core layer and outer core layer are formed from conventional thermoset rubber-based compositions as formulated in TABLE IV below. As shown in TABLE IV, core formulations 1 and 2 differ from each other at least by the amount of peroxide, the amount of zinc diacrylate, and presence/absence of an antioxidant:

TABLE IV GOLF BALL COMP. EX. 2 CORE LAYERS MATERIALS Ingredients OUTER CORE LAYER INNER CORE LAYER (Phr) (Core Formulation 1) (Core formulation 2) Polybutadiene 100 100 Zinc Oxide 5 5 Zinc diacrylate 35 31 (ZDA) Perkadox ® BC¹⁶ 0.5 * Trigonox ® 265¹⁷ * 1 Antioxidant * 0.4 ZnPCTP 0.5 0.5 ¹⁶Perkadox ® BC is an initiating agent (Dicumyl peroxide) available from Akzo Nobel. ¹⁷Trigonox ®265 is an initiating agent available from Akzo Nobel.

TABLE V incorporates the details of TABLE III and TABLE IV therein and further specifies the construction and certain additional properties for each of golf balls Ex. 5, Ex. 6, Ex. 7, Ex. 8 and Comp. Ex. 2:

TABLE V Golf Ball Construction EXAMPLES & Properties Ex. 5 Ex. 6 Ex. 7 Ex. 8 Comp. Ex. 2 Inner Core Elvax ® Nucrel ® Kraton ® Riteflex ® Core Material 150¹⁸ 9-1¹⁹ D0243 B²⁰ 425²¹ Formulation 2²² Inner Core 0.75 0.50 0.75 0.50 1.00 Diameter (in.) Center Hardness 26.8 48.6 35.5 43.3 71.0 (Shore C) Inner Core ≦40 ≦40 ≦40 ≦40 >40 Compression Outer Core TP₂ (1) TP₂ (2) TP₂ (3) TP₂ (4) Core Material Formulation 1²² Outer Core 0.400 0.525 0.400 0.525 0.275 Thickness (in.) Outer Core Surf. 84.5 91.5 91.1 88.6 87.5 Hardness (Shore C) Dual Core 65 98 69 89 88 Compression Intermediate Surlyn ® Surlyn ® Surlyn ® Surlyn ® Surlyn ® Layer Material 7940/8940²³ 7940/8940 7940/8940 7940/8940 7940/8940 Intermediate 0.035 0.035 0.035 0.035 0.035 Layer Thickness (in.) Intermediate 68.9 69.1 69.2 69.5 69.3 Layer Hardness (Shore D) Cover Material MDI²⁴/ MDI/ MDI/ MDI/ MDI/ PTMEG²⁵/ PTMEG/ PTMEG/ PTMEG/ PTMEG/ E-300²⁶ E-300 E-300 E-300 E-300 Cover Thickness 0.030 0.030 0.030 0.030 0.030 (in.) Cover Hardness 82.3 82.5 81.9 82.2 82.1 (Shore C) Ball Compression 72 110 79 91 99 ¹⁸Elvax ®150 is an ethylene-vinyl acetate copolymer resin (EVA) available from E. I. du Pont de Nemours and Company, Inc. ¹⁹Nucrel ®9-1 is an olefin-unsaturated carboxylic acid ester terpolymer available from E. I. du Pont de Nemours and Company, Inc. ²⁰Kraton ® D0243 B is a diblock copolymer based on styrene and butadiene with a polystyrene content of 33% (styrene block copolymer) available from Kraton Polymers. ²¹Riteflex ®425 is a thermoplastic polyester elastomer available from Ticona. ²²Core Formulations 1&2 as set forth in TABLE III above. ²³Surlyn ®7940 (Li) and Surlyn ®8940 (Na), are medium acid, monovalent and medium flow ionomers. ²⁴Methylene diphenyl diisocyanate. ²⁵Polytetramethylene ether glycol. ²⁶Ethacure 300, dimethylthiotoluene diamine, sold by Albemarle.

Referring to golf balls Ex. 5, Ex. 6, Ex. 7, and Ex. 8 of TABLE V, each dual core comprises a very soft, low compression inner core layer surrounded by a hard higher compression outer core layer. Additionally, each inner core layer has a diameter of less than 1.10 inches, is formed from an unfoamed thermoplastic composition, and has a center Shore C hardness of 50 or less.

Meanwhile, each outer core layer has a thickness of 0.200 inches or greater, is formed from a second thermoplastic composition that is different than the thermoplastic material of the inner core layer, and has an outer surface Shore C hardness of 80 or greater. Finally, in each of the dual cores of golf balls Ex. 5, Ex. 6, Ex. 7, and Ex. 8, the outer core layer has an outer surface hardness that is at least 40 Shore C points greater than the center hardness of the inner core layer.

Specifically referring to golf ball Ex. 5, the EVA inner core layer has a diameter of 0.75 in., and has a center Shore C hardness of 26.8. The outer core layer meanwhile has a thickness of 0.400 in., is formed from core formulation TP₂(1), and has an outer surface Shore C hardness of 84.5. The outer surface hardness of the outer core layer of golf ball Ex. 5 is therefore “at least 40 Shore C points greater than the center hardness of the inner core layer” (namely 57.7 Shore C points greater than the center hardness).

Notably, in golf ball Ex. 7, TP₂(3) differs from TP₂(1) of golf ball Ex. 5 at least in that TP₂(1) includes ethyl oleate, whereas TP₂(3) does not. Several property differences may also be noted between golf balls Ex. 7 and Ex. 5, respectively: inner core layer center Shore C hardnesses (35.5 versus 26.8); outer core layer surface Shore C hardnesses (91.1 versus 84.5); dual core compressions (69 versus 65); intermediate layer Shore D hardnesses (69.2 versus 68.9); cover layer surface shore C hardness (81.9 versus 82.3); and golf ball compression (79 versus 72). Nevertheless, golf ball Ex. 7 has an outer core layer outer surface hardness that is greater than the center hardness of the inner core layer by 55.6 Shore C hardness points, which is well above “at least 40 Shore C points greater”. Property difference between golf balls Ex. 7 and Ex. 5 may be attributed to the outer core layer formulation differences between TP₂(3) and TP₂(1) as well to the inner core material difference (styrene block copolymer versus EVA).

Regarding golf ball Ex. 8, it is also notable that TP₂(4) differs from TP₂(2) of golf ball Ex. 6 at least in that TP₂(4) includes a copolymer of ethylene and butyl acrylate, whereas TP₂(2) includes a styrene block copolymer instead. Several property differences may also be noted between golf balls Ex. 8 and Ex. 6, respectively: inner core layer center Shore C hardnesses (43.3 versus 48.6); outer core layer surface Shore C hardnesses (88.6 versus 91.5); dual core compressions (89 versus 98); intermediate layer Shore D hardnesses (69.5 versus 69.1); cover layer surface shore C hardness (82.2 versus 82.5); and golf ball compression (91 versus 110). Yet both golf balls Ex. 6 and Ex. 8 have a very high positive hardness gradient wherein the outer surface hardness of the outer core layer is at least 40 Shore C points greater than the center hardness of the inner core layer, namely by 42.9 and 45.7 Shore C hardness points, respectively. Once again, property difference between golf balls Ex. 8 and Ex. 6 may be attributed to the outer layer formulation difference between TP₂(4) and TP₂(2) as well as to the differing inner core materials (thermoplastic polyester elastomer versus olefin-unsaturated carboxylic acid ester terpolymer).

Comparative golf ball Comp. Ex. 2, unlike golf balls Ex. 5, Ex. 6, Ex. 7, and Ex. 8, incorporates conventional thermoset rubber-based compositions in both the inner core layer and an outer core layer. The inner core layer of Comp. Ex. 2 is formed from a conventional thermoset rubber-based composition having a center Shore C hardness well above 50 (namely 71). Meanwhile, the outer core layer of Comp. Ex. 2 has an outer surface Shore C hardness that is not “at least 40 Shore C points greater than the center hardness of the inner core layer” but rather, well below that, namely only 16.5 Shore C points greater. Furthermore,

Accordingly, each of golf balls Ex. 5, Ex. 6, Ex. 7, and Ex. 8 incorporates a core having a steep positive Shore C hardness gradient progressing from a hard core outer surface to a very soft center, whereas the core of golf ball Comp. Ex. 2 has a center Shore C hardness above 50 and a much more shallow Shore C hardness gradient from outer surface to center and well below “at least 40”.

In a golf ball of the invention, the solid inner core layer is formed from an unfoamed composition selected from thermoplastic compositions that can be formulated to provide a very soft, low compression center. Non-limiting examples of suitable inner core layer materials include Riteflex®425, Pebax® 2533 SA 01, Pebax® Rnew 25R53 SP 01, Kraton® D0243 B, Kraton® D1101 A, Kraton® D1101 B, Kraton® D1101 K, Kraton® D1102 K, Kraton® D1118 B, Estane® S180A TPU, Estane® S385A TPU, Estane T370A TPU, Estane® UB400 TPU, Fusbond® 525D, Fusabond® C190, Nucrel® 9-1, Elvax® 260, Elvax® 240W, Elvax® 150, and Elvax® 40W.

Thermoplastic compositions suitable for forming the inner core layer include ionomers; non-ionomeric acid polymers, such as E/Y- and E/X/Y-type copolymers, wherein E is an α-olefin (e.g., ethylene), Y is a carboxylic acid such as acrylic, methacrylic, crotonic, maleic, fumaric, or itaconic acid, and X is a softening comonomer such as vinyl esters of aliphatic carboxylic acids wherein the acid has from 2 to 10 carbons, alkyl ethers wherein the alkyl group has from 1 to 10 carbons, and alkyl alkylacrylates such as alkyl methacrylates wherein the alkyl group has from 1 to 10 carbons; polyurethanes, polyureas, and polyurethane-polyurea hybrids; polyester-based thermoplastic elastomers; polyamides, copolymers of ionomer and polyamide, polyamide-ethers, and polyamide-esters; ethylene-based homopolymers and copolymers; propylene-based homopolymers and copolymers; triblock copolymers based on styrene and ethylene/butylene; derivatives thereof that are compatibilized with at least one grafted or copolymerized functional group; and combinations of any two or more of the above thermoplastic polymers.

Ionomers, including partially neutralized ionomers and highly neutralized ionomers (HNPs), and ionomers formed from blends of two or more partially neutralized ionomers, blends of two or more highly neutralized ionomers, and blends of one or more partially neutralized ionomers with one or more highly neutralized ionomers, are particularly suitable for forming the core layers. For purposes of the present disclosure, “HNP” refers to an acid copolymer after at least 80% of all acid groups present in the composition are neutralized. Preferred ionomers are salts of E/X- and E/X/Y-type acid copolymers, wherein E is an α-olefin (e.g., ethylene), X is a C₃-C₈ α,β-ethylenically unsaturated carboxylic acid, and Y is a softening monomer. X is preferably selected from methacrylic acid, acrylic acid, ethacrylic acid, crotonic acid, and itaconic acid. Methacrylic acid and acrylic acid are particularly preferred. Y is preferably selected from (meth)acrylate and alkyl(meth)acrylates wherein the alkyl groups have from 1 to 8 carbon atoms, including, but not limited to, n-butyl (meth)acrylate, isobutyl(meth)acrylate, methyl (meth)acrylate, and ethyl (meth)acrylate. Particularly preferred E/X/Y-type copolymers are ethylene/(meth)acrylic acid/n-butyl (meth)acrylate, ethylene/(meth)acrylic acid/isobutyl(meth)acrylate, ethylene/(meth)acrylic acid/methyl (meth)acrylate, and ethylene/(meth)acrylic acid/ethyl (meth)acrylate. As used herein, “(meth)acrylic acid” means methacrylic acid and/or acrylic acid. Likewise, “(meth)acrylate” means methacrylate and/or acrylate. The α-olefin is typically present in the acid copolymer in an amount of 15 wt % or greater, or 25 wt % or greater, or 40 wt % or greater, or 60 wt % or greater, based on the total weight of the acid copolymer. The acid is typically present in the acid copolymer in an amount of 6 wt % or greater, or 9 wt % or greater, or 10 wt % or greater, or 11 wt % or greater, or 15 wt % or greater, or 16 wt % or greater, or in an amount within a range having a lower limit of 1 or 4 or 5 or 6 or 8 or 10 or 11 or 12 or 15 wt % and an upper limit of 15 or 16 or 17 or 19 or 20 or 20.5 or 21 or 25 or 30 or 35 or 40 wt %, based on the total weight of the acid copolymer. The optional softening monomer is typically present in the acid copolymer in an amount within a range having a lower limit of 0 or 1 or 3 or 5 or 11 or 15 or 20 wt % and an upper limit of 23 or 25 or 30 or 35 or 50 wt %, based on the total weight of the acid copolymer.

The acid copolymer is at least partially neutralized with a cation source, optionally in the presence of a high molecular weight organic acid, such as those disclosed in U.S. Pat. No. 6,756,436, the entire disclosure of which is hereby incorporated herein by reference. The acid copolymer can be reacted with the optional high molecular weight organic acid and the cation source simultaneously, or prior to the addition of the cation source. Suitable cation sources include, but are not limited to, metal ion sources, such as compounds of alkali metals, alkaline earth metals, transition metals, and rare earth elements; ammonium salts and monoamine salts; and combinations thereof. Preferred cation sources are compounds of magnesium, sodium, potassium, cesium, calcium, barium, manganese, copper, zinc, lead, tin, aluminum, nickel, chromium, lithium, and rare earth metals.

Suitable ionomers are further disclosed, for example, in U.S. Patent Application Publication Nos. 2005/0049367, 2005/0148725, 2005/0020741, 2004/0220343, and 2003/0130434, and U.S. Pat. Nos. 5,587,430, 5,691,418, 5,866,658, 6,100,321, 6,562,906, 6,653,382, 6,756,436, 6,777,472, 6,762,246, 6,815,480, 6,894,098, 6,919,393, 6,953,820, 6,994,638, 7,375,151, and 7,652,086, the entire disclosures of which are hereby incorporated herein by reference.

Thermoplastic compositions of the present invention optionally include additive(s) and/or filler(s) in an amount of 50 wt % or less, or 30 wt % or less, or 20 wt % or less, or 15 wt % or less, based on the total weight of the thermoplastic composition. Suitable additives and fillers include, but are not limited to, chemical blowing and foaming agents, optical brighteners, coloring agents, fluorescent agents, whitening agents, UV absorbers, light stabilizers, defoaming agents, processing aids, antioxidants, stabilizers, softening agents, fragrance components, plasticizers, impact modifiers, TiO₂, acid copolymer wax, surfactants, performance additives (e.g., A-C® performance additives, particularly A-C® low molecular weight ionomers and copolymers, A-C® oxidized polyethylenes, and A-C® ethylene vinyl acetate waxes, commercially available from Honeywell International Inc.), fatty acid amides (e.g., ethylene bis-stearamide and ethylene bis-oleamide), fatty acids and salts thereof (e.g., stearic acid, oleic acid, zinc stearate, magnesium stearate, zinc oleate, and magnesium oleate), and fillers, such as zinc oxide, tin oxide, barium sulfate, zinc sulfate, calcium oxide, calcium carbonate, zinc carbonate, barium carbonate, tungsten, tungsten carbide, silica, lead silicate, clay, mica, talc, nano-fillers, carbon black, glass flake, milled glass, flock, fibers, and mixtures thereof. Suitable additives are more fully described in, for example, U.S. Patent Application Publication No. 2003/0225197, the entire disclosure of which is hereby incorporated herein by reference. In a particular embodiment, the total amount of additive(s) and filler(s) present in the thermoplastic composition is 20 wt % or less, or 15 wt % or less, or 12 wt % or less, or 10 wt % or less, or 9 wt % or less, or 6 wt % or less, or 5 wt % or less, or 4 wt % or less, or 3 wt % or less, or within a range having a lower limit of 0 or 2 or 3 or 5 wt %, based on the total weight of the thermoplastic composition, and an upper limit of 9 or 10 or 12 or 15 or 20 wt %, based on the total weight of the thermoplastic composition. In a particular aspect of this embodiment, the thermoplastic composition includes filler(s) selected from carbon black, micro- and nano-scale clays and organoclays, including (e.g., Cloisite® and Nanofil® nanoclays, commercially available from Southern Clay Products, Inc.; Nanomax® and Nanomer® nanoclays, commercially available from Nanocor, Inc., and Perkalite® nanoclays, commercially available from Akzo Nobel Polymer Chemicals), micro- and nano-scale talcs (e.g., Luzenac HAR® high aspect ratio talcs, commercially available from Luzenac America, Inc.), glass (e.g., glass flake, milled glass, microglass, and glass fibers), micro- and nano-scale mica and mica-based pigments (e.g., Iriodin® pearl luster pigments, commercially available from The Merck Group), and combinations thereof. Particularly suitable combinations of fillers include, but are not limited to, micro-scale filler(s) combined with nano-scale filler(s), and organic filler(s) with inorganic filler(s).

Examples of commercially available thermoplastics suitable for forming the inner core layer include, but are not limited to, Surlyn® ionomer resins, Hytrel® thermoplastic polyester elastomers, ionomeric materials sold under the trade names DuPont® HPF 1000 and HPF 2000, Nucrel® acid copolymer resins, Fusabond® metallocene-catalyzed polyethylenes, Fusabond® functionalized ethylene acrylate copolymers, Fusabond® functionalized ethylene vinyl acetate copolymers, Fusabond® anhydride modified HDPEs, Fusabond® random ethylene copolymers, Fusabond® chemically modified ethylene elastomers, and Fusabond® functionalized polypropylenes, all of which are commercially available from E. I. du Pont de Nemours and Company; Iotek® ionomers, commercially available from ExxonMobil Chemical Company; Amplify® IO ionomers of ethylene acrylic acid copolymers, commercially available from The Dow Chemical Company; Clarix® ionomer resins, commercially available from A. Schulman Inc.; Elastollan® polyurethane-based thermoplastic elastomers, commercially available from BASF; Pebax® thermoplastic polyether and polyester amides, Lotader® ethylene/acrylic ester/maleic anhydride random terpolymers and Lotader® ethylene/ethyl acrylate/maleic anhydride random terpolymers, all of which are commercially available from Arkema Inc.; Kraton® linear triblock copolymers based on styrene and ethylene/butylene, commercially available from Kraton Performance Polymers Inc.; and Riteflex® polyester elastomers, commercially available from Ticona.

The inner and outer core layers of the type set forth in TABLE II are formulated to have different properties and they are formed from different types of compositions. For example, the inner core layer may be formed from an ionomer composition and the outer core layer is formed from a polybutadiene composition. Thermoset rubber compositions suitable for forming the outer core layer are those that can be formulated to provide an outer core surface hardness such that the core has an overall very high positive hardness gradient of at least 40 Shore C.

For example, the outer core layer core may be made from a composition including at least one thermoset base rubber, such as a polybutadiene rubber, cured with at least one peroxide and at least one reactive co-agent, which can be a metal salt of an unsaturated carboxylic acid, such as acrylic acid or methacrylic acid, a non-metallic coagent, or mixtures thereof. Preferably, a suitable antioxidant is included in the composition. An optional soft and fast agent (and sometimes a cis-to-trans catalyst), such as an organosulfur or metal-containing organosulfur compound, can also be included in the core formulation.

The degree of crosslinking of the rubber may be increased by increasing the amount (phr) of peroxide added. Meanwhile, zinc diacrylate is a coagent commonly used with peroxide to increase the state of cure, to take part in the cross-linking of polybutadiene. A small amount of ZDA and/or ZDMA produces a golf ball core with lower initial velocity and lower compression than a larger amount of coagent. The use of ZDA coagent may increase velocity and hardness and contribute to a hard feel. Thus, the amount of peroxide initiator and coagent can be varied to achieve a desired hardness. Antioxidants are compounds that inhibit or prevent the oxidative breakdown of elastomers, and/or inhibit or prevent reactions that are promoted by oxygen radicals.

Other ingredients that are known to those skilled in the art may be used, and are understood to include, but not be limited to, density-adjusting fillers, process aides, plasticizers, blowing or foaming agents, sulfur accelerators, and/or non-peroxide radical sources. The base thermoset rubber, which can be blended with other rubbers and polymers, typically includes a natural or synthetic rubber. A preferred base rubber is 1,4-polybutadiene having a cis structure of at least 40%, preferably greater than 80%, and more preferably greater than 90%. Examples of desirable polybutadiene rubbers include BUNA® CB22 and BUNA® CB23, commercially available from LANXESS Corporation; UBEPOL® 360L and UBEPOL® 150L and UBEPOL-BR rubbers, commercially available from UBE Industries, Ltd. of Tokyo, Japan; BUDENE 1208, 1207, commercially available from Goodyear of Akron, Ohio; and CB BUNA® 1203G1, 1220, and 1221, commercially available from LANXESS Corporation; Europrene® NEOCIS® BR 40 and BR 60, commercially available from Polimeri Europa; and BR 01, BR 730, BR 735, BR 11, and BR 51, commercially available from Japan Synthetic Rubber Co., Ltd; and KARBOCHEM® ND40, ND45, and ND60, commercially available from Karbochem.

The base rubber may also comprise high or medium Mooney viscosity rubber, or blends thereof. A “Mooney” unit is a unit used to measure the resistance to flow of raw or unvulcanized rubber. The viscosity in a “Mooney” unit is equal to the torque, measured on an arbitrary scale, on a disk in a vessel that contains rubber at a temperature of 100° C. and rotates at two revolutions per minute. The measurement of Mooney viscosity is defined according to ASTM D-1646.

The Mooney viscosity range is preferably greater than about 40, more preferably in the range from about 40 to about 80 and more preferably in the range from about 40 to about 60. Polybutadiene rubber with higher Mooney viscosity may also be used, so long as the viscosity of the polybutadiene does not reach a level where the high viscosity polybutadiene adversely interferes with the manufacturing machinery. It is contemplated that polybutadiene with viscosity less than 65 Mooney can be used with the present invention.

In one embodiment of the present invention, golf ball cores made with mid- to high-Mooney viscosity polybutadiene material exhibit increased resiliency (and, therefore, distance) without increasing the hardness of the ball. Such cores are soft, i.e., compression less than about 60 and more specifically in the range of about 50-55. Cores with compression in the range of from about 30 about 50 are also within the range of this preferred embodiment.

Commercial sources of suitable mid- to high-Mooney viscosity polybutadiene include LANXESS CB23 (Nd-catalyzed), which has a Mooney viscosity of around 50 and is a highly linear polybutadiene. If desired, the polybutadiene can also be mixed with other elastomers known in the art, such as other polybutadiene rubbers, natural rubber, styrene butadiene rubber, and/or isoprene rubber in order to further modify the properties of the core. When a mixture of elastomers is used, the amounts of other constituents in the core composition are typically based on 100 parts by weight of the total elastomer mixture.

In one preferred embodiment, the base rubber comprises an Nd-catalyzed polybutadiene, a non-rare earth-catalyzed polybutadiene rubber, or blends thereof. If desired, the polybutadiene can also be mixed with other elastomers known in the art such as natural rubber, polyisoprene rubber and/or styrene-butadiene rubber in order to modify the properties of the core. Other suitable base rubbers include thermosetting materials such as, ethylene propylene diene monomer rubber, ethylene propylene rubber, butyl rubber, halobutyl rubber, hydrogenated nitrile butadiene rubber, nitrile rubber, and silicone rubber.

Thermoplastic elastomers (TPE) may also be used to modify the properties of the core layers, or the uncured core layer stock by blending with the base thermoset rubber. These TPEs include styrenic block copolymers, such as styrene ethylene butadiene styrene, styrene-isoprene-styrene, etc., a metallocene or other single-site catalyzed polyolefin such as ethylene-octene, or ethylene-butene, or thermoplastic polyurethanes (TPU), including copolymers. Other suitable TPEs for blending with the thermoset rubbers of the present invention include PEBAX®, which is believed to comprise polyether amide copolymers, HYTREL®, which is believed to comprise polyether ester copolymers, thermoplastic urethane, and KRATON®, which is believed to comprise styrenic block copolymers elastomers. Any of the TPEs or TPUs above may also contain functionality suitable for grafting, including maleic acid or maleic anhydride.

Additional polymers may also optionally be incorporated into the base rubber. Examples include, but are not limited to, thermoset elastomers such as core regrind, thermoplastic vulcanizate, copolymeric ionomer, terpolymeric ionomer, polycarbonate, polyamide, copolymeric polyamide, polyesters, polyvinyl alcohols, acrylonitrile-butadiene-styrene copolymers, polyarylate, polyacrylate, polyphenylene ether, impact-modified polyphenylene ether, high impact polystyrene, diallyl phthalate polymer, styrene-acrylonitrile polymer (SAN) (including olefin-modified SAN and acrylonitrile-styrene-acrylonitrile polymer), styrene-maleic anhydride copolymer, styrenic copolymer, functionalized styrenic copolymer, functionalized styrenic terpolymer, styrenic terpolymer, cellulose polymer, liquid crystal polymer, ethylene-vinyl acetate copolymers, polyurea, and polysiloxane or any metallocene-catalyzed polymers of these species.

Suitable polyamides for use as an additional polymeric material in compositions within the scope of the present invention also include resins obtained by: (1) polycondensation of (a) a dicarboxylic acid, such as oxalic acid, adipic acid, sebacic acid, terephthalic acid, isophthalic acid, or 1,4-cyclohexanedicarboxylic acid, with (b) a diamine, such as ethylenediamine, tetramethylenediamine, pentamethylenediamine, hexamethylenediamine, or decamethylenediamine, 1,4-cyclohexanediamine, or m-xylylenediamine; (2) a ring-opening polymerization of cyclic lactam, such as ε-caprolactam or Ω-laurolactam; (3) polycondensation of an aminocarboxylic acid, such as 6-aminocaproic acid, 9-aminononanoic acid, 11-aminoundecanoic acid, or 12-aminododecanoic acid; or (4) copolymerization of a cyclic lactam with a dicarboxylic acid and a diamine. Specific examples of suitable polyamides include NYLON 6, NYLON 66, NYLON 610, NYLON 11, NYLON 12, copolymerized NYLON, NYLON MXD6, and NYLON 46.

Suitable peroxide initiating agents include dicumyl peroxide; 2,5-dimethyl-2,5-di(t-butylperoxy) hexane; 2,5-dimethyl-2,5-di(t-butylperoxy)hexyne; 2,5-dimethyl-2,5-di(benzoylperoxy)hexane; 2,2′-bis(t-butylperoxy)-di-iso-propylbenzene; 1,1-bis(t-butylperoxy)-3,3,5-trimethyl cyclohexane; n-butyl 4,4-bis(t-butyl-peroxy)valerate; t-butyl perbenzoate; benzoyl peroxide; n-butyl 4,4′-bis(butylperoxy) valerate; di-t-butyl peroxide; or 2,5-di-(t-butylperoxy)-2,5-dimethyl hexane, lauryl peroxide, t-butyl hydroperoxide, α-α bis(t-butylperoxy)diisopropylbenzene, di(2-t-butyl-peroxyisopropyl)benzene, di-t-amyl peroxide, di-t-butyl peroxide. Preferably, the rubber composition includes from about 0.25 to about 5.0 parts by weight peroxide per 100 parts by weight rubber (phr), more preferably 0.5 phr to 3 phr, most preferably 0.5 phr to 1.5 phr. In a most preferred embodiment, the peroxide is present in an amount of about 0.8 phr. These ranges of peroxide are given assuming the peroxide is 100% active, without accounting for any carrier that might be present. Because many commercially available peroxides are sold along with a carrier compound, the actual amount of active peroxide present must be calculated. Commercially-available peroxide initiating agents include DICUP™ family of dicumyl peroxides (including DICUP™ R, DICUP™ 40C and DICUP™ 40KE) available from ARKEMA. Similar initiating agents are available from AkroChem, Lanxess, Flexsys/Harwick and R.T. Vanderbilt. Another commercially-available and preferred initiating agent is TRIGONOX™ 265-50B from Akzo Nobel, which is a mixture of 1,1-di(t-butylperoxy)-3,3,5-trimethylcyclohexane and di(2-t-butylperoxyisopropyl)benzene. TRIGONOX™ peroxides are generally sold on a carrier compound.

Suitable reactive co-agents include, but are not limited to, metal salts of diacrylates, dimethacrylates, and monomethacrylates suitable for use in this invention include those wherein the metal is zinc, magnesium, calcium, barium, tin, aluminum, lithium, sodium, potassium, iron, zirconium, and bismuth. Zinc diacrylate (ZDA) is preferred, but the present invention is not limited thereto. ZDA provides golf balls with a high initial velocity. The ZDA can be of various grades of purity. For the purposes of this invention, the lower the quantity of zinc stearate present in the ZDA the higher the ZDA purity. ZDA containing less than about 10% zinc stearate is preferable. More preferable is ZDA containing about 4-8% zinc stearate. Suitable, commercially available zinc diacrylates include those from Cray Valley. The preferred concentrations of ZDA that can be used are about 10 phr to about 40 phr, more preferably 20 phr to about 35 phr, most preferably 25 phr to about 35 phr. In a particularly preferred embodiment, the reactive co-agent is present in an amount of about 29 phr to about 31 phr.

Additional preferred co-agents that may be used alone or in combination with those mentioned above include, but are not limited to, trimethylolpropane trimethacrylate, trimethylolpropane triacrylate, and the like. It is understood by those skilled in the art, that in the case where these co-agents may be liquids at room temperature, it may be advantageous to disperse these compounds on a suitable carrier to promote ease of incorporation in the rubber mixture.

Antioxidants are compounds that inhibit or prevent the oxidative breakdown of elastomers, and/or inhibit or prevent reactions that are promoted by oxygen radicals. Some exemplary antioxidants that may be used in the present invention include, but are not limited to, quinoline type antioxidants, amine type antioxidants, and phenolic type antioxidants. A preferred antioxidant is 2,2′-methylene-bis-(4-methyl-6-t-butylphenol) available as VANOX® MBPC from R.T. Vanderbilt. Other polyphenolic antioxidants include VANOX® T, VANOX® L, VANOX® SKT, VANOX® SWP, VANOX® 13 and VANOX® 1290.

Suitable antioxidants include, but are not limited to, alkylene-bis-alkyl substituted cresols, such as 4,4′-methylene-bis(2,5-xylenol); 4,4′-ethylidene-bis-(6-ethyl-m-cresol); 4,4′-butylidene-bis-(6-t-butyl-m-cresol); 4,4′-decylidene-bis-(6-methyl-m-cresol); 4,4′-methylene-bis-(2-amyl-m-cresol); 4,4′-propylidene-bis-(5-hexyl-m-cresol); 3,3′-decylidene-bis-(5-ethyl-p-cresol); 2,2′-butylidene-bis-(3-n-hexyl-p-cresol); 4,4′-(2-butylidene)-bis-(6-t-butyl-m-cresol); 3,3′-4(decylidene)-bis-(5-ethyl-p-cresol); (2,5-dimethyl-4-hydroxyphenyl) (2-hydroxy-3,5-dimethylphenyl) methane; (2-methyl-4-hydroxy-5-ethylphenyl) (2-ethyl-3-hydroxy-5-methylphenyl) methane; (3-methyl-5-hydroxy-6-t-butylphenyl) (2-hydroxy-4-methyl-5-decylphenyl)-n-butyl methane; (2-hydroxy-4-ethyl-5-methylphenyl) (2-decyl-3-hydroxy-4-methylphenyl)butylamylmethane; (3-ethyl-4-methyl-5-hydroxyphenyl)-(2,3-dimethyl-3-hydroxy-phenyl)nonylmethane; (3-methyl-2-hydroxy-6-ethylphenyl)-(2-isopropyl-3-hydroxy-5-methyl-phenyl)cyclohexylmethane; (2-methyl-4-hydroxy-5-methylphenyl) (2-hydroxy-3-methyl-5-ethylphenyl)dicyclohexyl methane; and the like.

Other suitable antioxidants include, but are not limited to, substituted phenols, such as 2-tert-butyl-4-methoxyphenol; 3-tert-butyl-4-methoxyphenol; 3-tert-octyl-4-methoxyphenol; 2-methyl-4-methoxyphenol; 2-stearyl-4-n-butoxyphenol; 3-t-butyl-4-stearyloxyphenol; 3-lauryl-4-ethoxyphenol; 2,5-di-t-butyl-4-methoxyphenol; 2-methyl-4-methoxyphenol; 2-(1-methycyclohexyl)-4-methoxyphenol; 2-t-butyl-4-dodecyloxyphenol; 2-(1-methylbenzyl)-4-methoxyphenol; 2-t-octyl-4-methoxyphenol; methyl gallate; n-propyl gallate; n-butyl gallate; lauryl gallate; myristyl gallate; stearyl gallate; 2,4,5-trihydroxyacetophenone; 2,4,5-trihydroxy-n-butyrophenone; 2,4,5-trihydroxystearophenone; 2,6-ditert-butyl-4-methylphenol; 2,6-ditert-octyl-4-methylphenol; 2,6-ditert-butyl-4-stearylphenol; 2-methyl-4-methyl-6-tert-butylphenol; 2,6-distearyl-4-methylphenol; 2,6-dilauryl-4-methylphenol; 2,6-di(n-octyl)-4-methylphenol; 2,6-di(n-hexadecyl)-4-methylphenol; 2,6-di(1-methylundecyl)-4-methylphenol; 2,6-di(1-methylheptadecyl)-4-methylphenol; 2,6-di(trimethylhexyl)-4-methylphenol; 2,6-di(1,1,3,3-tetramethyloctyl)-4-methylphenol; 2-n-dodecyl-6-tert butyl-4-methylphenol; 2-n-dodecyl-6-(1-methylundecyl)-4-methylphenol; 2-n-dodecyl-6-(1,1,3,3-tetramethyloctyl)-4-methylphenol; 2-n-dodecyl-6-n-octadecyl-4-methylphenol; 2-n-dodecyl-6-n-octyl-4-methylphenol; 2-methyl-6-n-octadecyl-4-methylphenol; 2-n-dodecyl-6-(1-methylheptadecyl)-4-methylphenol; 2,6-di(1-methylbenzyl)-4-methylphenol; 2,6-di(1-methylcyclohexyl)-4-methylphenol; 2,6-(1-methylcyclohexyl)-4-methylphenol; 2-(1-methylbenzyl)-4-methylphenol; and related substituted phenols.

More suitable antioxidants include, but are not limited to, alkylene bisphenols, such as 4,4′-butylidene bis(3-methyl-6-t-butyl phenol); 2,2-butylidene bis(4,6-dimethyl phenol); 2,2′-butylidene bis(4-methyl-6-t-butyl phenol); 2,2′-butylidene bis(4-t-butyl-6-methyl phenol); 2,2′-ethylidene bis(4-methyl-6-t-butylphenol); 2,2′-methylene bis(4,6-dimethyl phenol); 2,2′-methylene bis(4-methyl-6-t-butyl phenol); 2,2′-methylene bis(4-ethyl-6-t-butyl phenol); 4,4′-methylene bis(2,6-di-t-butyl phenol); 4,4′-methylene bis(2-methyl-6-t-butyl phenol); 4,4′-methylene bis(2,6-dimethyl phenol); 2,2′-methylene bis(4-t-butyl-6-phenyl phenol); 2,2′-dihydroxy-3,3′,5,5′-tetramethylstilbene; 2,2′-isopropylidene bis(4-methyl-6-t-butyl phenol); ethylene bis(beta-naphthol); 1,5-dihydroxy naphthalene; 2,2′-ethylene bis(4-methyl-6-propyl phenol); 4,4′-methylene bis(2-propyl-6-t-butyl phenol); 4,4′-ethylene bis(2-methyl-6-propyl phenol); 2,2′-methylene bis(5-methyl-6-t-butyl phenol); and 4,4′-butylidene bis(6-t-butyl-3-methyl phenol);

Suitable antioxidants further include, but are not limited to, alkylene trisphenols, such as 2,6-bis(2′-hydroxy-3′-t-butyl-5′-methyl benzyl)-4-methyl phenol; 2,6-bis(2′-hydroxy-3′-t-ethyl-5′-butyl benzyl)-4-methyl phenol; and 2,6-bis(2′-hydroxy-3′-t-butyl-5′-propyl benzyl)-4-methyl phenol.

The antioxidant is typically present in an amount of about 0.1 phr to about 5 phr, preferably from about 0.1 phr to about 2 phr, more preferably about 0.1 phr to about 1 phr. In a particularly preferred embodiment, the antioxidant is present in an amount of about 0.4 phr. In an alternative embodiment, the antioxidant should be present in an amount to ensure that the hardness gradient of the inventive cores is negative. Preferably, about 0.2 phr to about 1 phr antioxidant is added to the core layer (inner core or outer core layer) formulation, more preferably, about 0.3 to about 0.8 phr, and most preferably 0.4 to about 0.7 phr. Preferably, about 0.25 phr to about 1.5 phr of peroxide as calculated at 100% active can be added to the core formulation, more preferably about 0.5 phr to about 1.2 phr, and most preferably about 0.7 phr to about 1.0 phr. The ZDA amount can be varied to suit the desired compression, spin and feel of the resulting golf ball. The cure regime can have a temperature range between from about 290° F. to about 360° F., or from about 290° F. to about 335° F., or from about 300° F. to about 325° F., or from about 330° F. to about 355° F., and the stock is held at that temperature for at least about 10 minutes to about 30 minutes.

The thermoset rubber composition in a core of the golf ball of the present invention may also include an optional soft and fast agent. As used herein, “soft and fast agent” means any compound or a blend thereof that that is capable of making a core 1) be softer (lower compression) at constant COR or 2) have a higher COR at equal compression, or any combination thereof, when compared to a core equivalently prepared without a soft and fast agent. Preferably, the composition of the present invention contains from about 0.05 phr to about 10.0 phr soft and fast agent. In one embodiment, the soft and fast agent is present in an amount of about 0.05 phr to about 3.0 phr, preferably about 0.05 phr to about 2.0 phr, more preferably about 0.05 phr to about 1.0 phr. In another embodiment, the soft and fast agent is present in an amount of about 2.0 phr to about 5.0 phr, preferably about 2.35 phr to about 4.0 phr, and more preferably about 2.35 phr to about 3.0 phr. In an alternative high concentration embodiment, the soft and fast agent is present in an amount of about 5.0 phr to about 10.0 phr, more preferably about 6.0 phr to about 9.0 phr, most preferably about 7.0 phr to about 8.0 phr. In a most preferred embodiment, the soft and fast agent is present in an amount of about 2.6 phr.

Suitable soft and fast agents include, but are not limited to, organosulfur or metal-containing organosulfur compounds, an organic sulfur compound, including mono, di, and polysulfides, a thiol, or mercapto compound, an inorganic sulfide compound, a Group VIA compound, or mixtures thereof. The soft and fast agent component may also be a blend of an organosulfur compound and an inorganic sulfide compound.

Suitable soft and fast agents of the present invention include, but are not limited to those having the following general formula:

where R₁-R₅ can be C₁-C₈ alkyl groups; halogen groups; thiol groups (—SH), carboxylated groups; sulfonated groups; and hydrogen; in any order; and also pentafluorothiophenol; 2-fluorothiophenol; 3-fluorothiophenol; 4-fluorothiophenol; 2,3-fluorothiophenol; 2,4-fluorothiophenol; 3,4-fluorothiophenol; 3,5-fluorothiophenol 2,3,4-fluorothiophenol; 3,4,5-fluorothiophenol; 2,3,4,5-tetrafluorothiophenol; 2,3,5,6-tetrafluorothiophenol; 4-chlorotetrafluorothiophenol; pentachlorothiophenol; 2-chlorothiophenol; 3-chlorothiophenol; 4-chlorothiophenol; 2,3-chlorothiophenol; 2,4-chlorothiophenol; 3,4-chlorothiophenol; 3,5-chlorothiophenol; 2,3,4-chlorothiophenol; 3,4,5-chlorothiophenol; 2,3,4,5-tetrachlorothiophenol; 2,3,5,6-tetrachlorothiophenol; pentabromothiophenol; 2-bromothiophenol; 3-bromothiophenol; 4-bromothiophenol; 2,3-bromothiophenol; 2,4-bromothiophenol; 3,4-bromothiophenol; 3,5-bromothiophenol; 2,3,4-bromothiophenol; 3,4,5-bromothiophenol; 2,3,4,5-tetrabromothiophenol; 2,3,5,6-tetrabromothiophenol; pentaiodothiophenol; 2-iodothiophenol; 3-iodothiophenol; 4-iodothiophenol; 2,3-iodothiophenol; 2,4-iodothiophenol; 3,4-iodothiophenol; 3,5-iodothiophenol; 2,3,4-iodothiophenol; 3,4,5-iodothiophenol; 2,3,4,5-tetraiodothiophenol; 2,3,5,6-tetraiodothiophenoland; and their zinc salts. Preferably, the halogenated thiophenol compound is pentachlorothiophenol, which is commercially available in neat form or under the tradename STRUKTOL®, a clay-based carrier containing the sulfur compound pentachlorothiophenol loaded at 45 percent (correlating to 2.4 parts PCTP). STRUKTOL® is commercially available from Struktol Company of America of Stow, Ohio. PCTP is commercially available in neat form from eChinachem of San Francisco, Calif. and in the salt form from eChinachem of San Francisco, Calif. Most preferably, the halogenated thiophenol compound is the zinc salt of pentachlorothiophenol, which is commercially available from eChinachem of San Francisco, Calif.

As used herein when referring to the invention, the term “organosulfur compound(s)” refers to any compound containing carbon, hydrogen, and sulfur, where the sulfur is directly bonded to at least 1 carbon. As used herein, the term “sulfur compound” means a compound that is elemental sulfur, polymeric sulfur, or a combination thereof. It should be further understood that the term “elemental sulfur” refers to the ring structure of S₈ and that “polymeric sulfur” is a structure including at least one additional sulfur relative to elemental sulfur.

Additional suitable examples of soft and fast agents (that are also believed to be cis-to-trans catalysts) include, but are not limited to, 4,4′-diphenyl disulfide; 4,4′-ditolyl disulfide; 2,2′-benzamido diphenyl disulfide; bis(2-aminophenyl)disulfide; bis(4-aminophenyl)disulfide; bis(3-aminophenyl)disulfide; 2,2′-bis(4-aminonaphthyl)disulfide; 2,2′-bis(3-aminonaphthyl)disulfide; 2,2′-bis(4-aminonaphthyl)disulfide; 2,2′-bis(5-aminonaphthyl)disulfide; 2,2′-bis(6-aminonaphthyl)disulfide; 2,2′-bis(7-aminonaphthyl)disulfide; 2,2′-bis(8-aminonaphthyl) disulfide; 1,1′-bis(2-aminonaphthyl)disulfide; 1,1′-bis(3-aminonaphthyl)disulfide; 1,1′-bis(3-aminonaphthyl)disulfide; 1,1′-bis(4-aminonaphthyl)disulfide; 1,1′-bis(5-aminonaphthyl)disulfide; 1,1′-bis(6-aminonaphthyl)disulfide; 1,1′-bis(7-aminonaphthyl)disulfide; 1,1′-bis(8-aminonaphthyl)disulfide; 1,2′-diamino-1,2′-dithiodinaphthalene; 2,3′-diamino-1,2′-dithiodinaphthalene; bis(4-chlorophenyl)disulfide; bis(2-chlorophenyl)disulfide; bis(3-chlorophenyl)disulfide; bis(4-bromophenyl)disulfide; bis(2-bromophenyl)disulfide; bis(3-bromophenyl)disulfide; bis(4-fluorophenyl)disulfide; bis(4-iodophenyl)disulfide; bis(2,5-dichlorophenyl)disulfide; bis(3,5-dichlorophenyl)disulfide; bis(2,4-dichlorophenyl)disulfide; bis(2,6-dichlorophenyl)disulfide; bis(2,5-dibromophenyl)disulfide; bis(3,5-dibromophenyl)disulfide; bis(2-chloro-5-bromophenyl)disulfide; bis(2,4,6-trichlorophenyl)disulfide; bis(2,3,4,5,6-pentachlorophenyl)disulfide; bis(4-cyanophenyl)disulfide; bis(2-cyanophenyl)disulfide; bis(4-nitrophenyl)disulfide; bis(2-nitrophenyl)disulfide; 2,2′-dithiobenzoic acid ethylester; 2,2′-dithiobenzoic acid methylester; 2,2′-dithiobenzoic acid; 4,4′-dithiobenzoic acid ethylester; bis(4-acetylphenyl)disulfide; bis(2-acetylphenyl)disulfide; bis(4-formylphenyl)disulfide; bis(4-carbamoylphenyl)disulfide; 1,1′-dinaphthyl disulfide; 2,2′-dinaphthyl disulfide; 1,2′-dinaphthyl disulfide; 2,2′-bis(1-chlorodinaphthyl)disulfide; 2,2′-bis(1-bromonaphthyl)disulfide; 1,1′-bis(2-chloronaphthyl)disulfide; 2,2′-bis(1-cyanonaphthyl)disulfide; 2,2′-bis(1-acetylnaphthyl)disulfide; and the like; or a mixture thereof. Preferred organosulfur components include 4,4′-diphenyl disulfide, 4,4′-ditolyl disulfide, or 2,2′-benzamido diphenyl disulfide, or a mixture thereof. A more preferred organosulfur component includes 4,4′-ditolyl disulfide. In another embodiment, metal-containing organosulfur components can be used according to the invention. Suitable metal-containing organosulfur components include, but are not limited to, cadmium, copper, lead, and tellurium analogs of diethyldithiocarbamate, diamyldithiocarbamate, and dimethyldithiocarbamate, or mixtures thereof.

Suitable substituted or unsubstituted aromatic organic components that do not include sulfur or a metal include, but are not limited to, 4,4′-diphenyl acetylene, azobenzene, or a mixture thereof. The aromatic organic group preferably ranges in size from C₆ to C₂₀, and more preferably from C₆ to C₁₀. Suitable inorganic sulfide components include, but are not limited to titanium sulfide, manganese sulfide, and sulfide analogs of iron, calcium, cobalt, molybdenum, tungsten, copper, selenium, yttrium, zinc, tin, and bismuth.

A substituted or unsubstituted aromatic organic compound is also suitable as a soft and fast agent. Suitable substituted or unsubstituted aromatic organic components include, but are not limited to, components having the formula (R₁)_(x)—R₃-M-R₄—(R₂)_(y), wherein R₁ and R₂ are each hydrogen or a substituted or unsubstituted C₁₋₂₀ linear, branched, or cyclic alkyl, alkoxy, or alkylthio group, or a single, multiple, or fused ring C₆ to C₂₄ aromatic group; x and y are each an integer from 0 to 5; R₃ and R₄ are each selected from a single, multiple, or fused ring C₆ to C₂₄ aromatic group; and M includes an azo group or a metal component. R₃ and R₄ are each preferably selected from a C₆ to C₁₀ aromatic group, more preferably selected from phenyl, benzyl, naphthyl, benzamido, and benzothiazyl. R₁ and R₂ are each preferably selected from a substituted or unsubstituted C₁₋₁₀ linear, branched, or cyclic alkyl, alkoxy, or alkylthio group or a C₆ to C₁₀ aromatic group. When R₁, R₂, R₃, or R₄, are substituted, the substitution may include one or more of the following substituent groups: hydroxy and metal salts thereof; mercapto and metal salts thereof; halogen; amino, nitro, cyano, and amido; carboxyl including esters, acids, and metal salts thereof; silyl; acrylates and metal salts thereof; sulfonyl or sulfonamide; and phosphates and phosphites. When M is a metal component, it may be any suitable elemental metal available to those of ordinary skill in the art. Typically, the metal will be a transition metal, although preferably it is tellurium or selenium. In one embodiment, the aromatic organic compound is substantially free of metal, while in another embodiment the aromatic organic compound is completely free of metal.

The soft and fast agent can also include a Group VIA component. Elemental sulfur and polymeric sulfur are commercially available from Elastochem, Inc. of Chardon, Ohio Exemplary sulfur catalyst compounds include PB(RM-S)-80 elemental sulfur and PB(CRST)-65 polymeric sulfur, each of which is available from Elastochem, Inc. An exemplary tellurium catalyst under the tradename TELLOY® and an exemplary selenium catalyst under the tradename VANDEX® are each commercially available from RT Vanderbilt.

Fillers may also be added to the thermoset rubber composition of the core to adjust the density of the composition, up or down. Typically, fillers include materials such as tungsten, zinc oxide, barium sulfate, silica, calcium carbonate, zinc carbonate, metals, metal oxides and salts, regrind (recycled core material typically ground to about 30 mesh particle), high-Mooney-viscosity rubber regrind, trans-regrind core material (recycled core material containing high trans-isomer of polybutadiene), and the like. When trans-regrind is present, the amount of trans-isomer is preferably between about 10% and about 60%. In a preferred embodiment of the invention, the core comprises polybutadiene having a cis-isomer content of greater than about 95% and trans-regrind core material (already vulcanized) as a filler. Any particle size trans-regrind core material is sufficient, but is preferably less than about 125 μm.

Fillers added to one or more portions of the golf ball typically include processing aids or compounds to affect rheological and mixing properties, density-modifying fillers, tear strength, or reinforcement fillers, and the like. The fillers are generally inorganic, and suitable fillers include numerous metals or metal oxides, such as zinc oxide and tin oxide, as well as barium sulfate, zinc sulfate, calcium carbonate, barium carbonate, clay, tungsten, tungsten carbide, an array of silicas, and mixtures thereof. Fillers may also include various foaming agents or blowing agents which may be readily selected by one of ordinary skill in the art. Fillers may include polymeric, ceramic, metal, and glass microspheres may be solid or hollow, and filled or unfilled. Fillers are typically also added to one or more portions of the golf ball to modify the density thereof to conform to uniform golf ball standards. Fillers may also be used to modify the weight of the center or at least one additional layer for specialty balls, e.g., a lower weight ball is preferred for a player having a low swing speed.

Materials such as tungsten, zinc oxide, barium sulfate, silica, calcium carbonate, zinc carbonate, metals, metal oxides and salts, and regrind (recycled core material typically ground to about 30 mesh particle) are also suitable fillers.

The polybutadiene and/or any other base rubber or elastomer system may also be foamed, or filled with hollow microspheres or with expandable microspheres which expand at a set temperature during the curing process to any low specific gravity level. Other ingredients such as sulfur accelerators, e.g., tetramethylthiuram di, tri, or tetrasulfide, and/or metal-containing organosulfur components may also be used according to the invention. Suitable metal-containing organosulfur accelerators include, but are not limited to, cadmium, copper, lead, and tellurium analogs of diethyldithiocarbamate, diamyldithiocarbamate, and dimethyldithiocarbamate, or mixtures thereof. Other ingredients such as processing aids e.g., fatty acids and/or their metal salts, processing oils, dyes and pigments, as well as other additives known to one skilled in the art may also be used in the present invention in amounts sufficient to achieve the purpose for which they are typically used.

Without being bound by theory, it is believed that the percentage of double bonds in the trans configuration may be manipulated throughout a core containing at least one main-chain unsaturated rubber (i.e., polybutadiene), plastic, or elastomer resulting in a trans gradient. The trans gradient may be influenced (up or down) by changing the type and amount of cis-to-trans catalyst (or soft-and-fast agent), the type and amount of peroxide, and the type and amount of coagent in the formulation. For example, a formulation containing about 0.25 phr ZnPCTP may have a trans gradient of about 5% across the core whereas a formulation containing about 2 phr ZnPCTP may have a trans gradient of about 10%, or higher. The trans gradient may also be manipulated through the cure times and temperatures. It is believed that lower temperatures and shorter cure times yield lower trans gradients, although a combination of many of these factors may yield gradients of differing and/or opposite directions from that resulting from use of a single factor.

In general, higher and/or faster cure rates tend to yield higher levels of trans content, as do higher concentrations of peroxides, soft-and-fast agents, and, to some extent, ZDA concentration. Even the type of rubber may have an effect on trans levels, with those catalyzed by rare-earth metals, such as Nd, being able to form higher levels of trans polybutadiene compared to those rubbers formed from Group VIII metals, such as Co, Ni, and Li.

Meanwhile, in a different embodiment, the thermoplastic inner and outer core layers of a golf ball of the invention of the type set forth in TABLE V are also formulated to have properties that differ as disclosed herein. Non-limiting examples of suitable thermoplastic materials for an inner core layer and outer core layer of a golf ball of the invention in this embodiment appear in TABLE V and elsewhere herein.

Two further different constructions are illustrated in prophetic golf balls Ex. 9 and Ex. 10 below and compared with one conventional prophetic golf ball Comp. Ex. 3. Each of golf balls Ex. 9 and Ex. 10 incorporate an inner core layer TPp formed from a plasticized thermoplastic composition and an outer core layer formed from at least one of a thermoset rubber composition and a thermoplastic composition TP that is not plasticized, as follows.

Prophetic inventive golf balls Ex. 9, Ex. 10 and comparative prophetic golf ball Comp. Ex. 3 each comprise a core, a cover, and an intermediate layer disposed between the core and the cover. Additionally, every core is a dual core comprising an inner core layer surrounded by an outer core layer.

The inner core layers of inventive prophetic golf balls Ex. 9 and Ex. 10 are each formed from a different plasticized thermoplastic material TP_(p) as formulated in TABLE VI:

TABLE VI INNER CORE LAYER MATERIALS (TP_(p)) Ingredients Ex. 9 Ex. 10 (Phr) TP_(p)(1) TP_(p)(2) HPF2000²⁷ 70 HPC AD1022²⁸ 90 Butyl Oleate 10 2-EthylhexylOleate 30 ²⁷DuPont ® HPF2000 is an ionomer of ethylene acid and terpolymer commercially available from E. I. du Pont de Nemours and Company. ²⁸DuPont ® HPC AD1022 is an ionomer resin commercially available from E. I. du Pont de Nemours and Company.

In turn, the outer core layers of golf balls Ex. 9 and Ex. 10 are each formed from a different thermoset rubber composition 2 and 1, respectively, as formulated in TABLE VII:

TABLE VII THERMOSET OUTER CORE MATERIALS INGREDIENTS Core Core Core (Phr) Formulation 1 Formulation 2 formulation 3 Polybutadiene 100 100 100 Zinc Oxide 5 5 5 Zinc diacrylate 35 38 31 (ZDA) Perkadox ® BC²⁹ 0.5 0.5 * Trigonox ® 265³⁰ * * 1 Antioxidant * * 0.4 ZnPCTP 0.5 0.5 0.5 ²⁹Perkadox ® BC is an initiating agent (Dicumyl peroxide) available from Akzo Nobel. ³⁰Trigonox ®265 is an initiating agent available from Akzo Nobel.

Meanwhile, in comparative golf ball Comp. Ex. 3, both the inner core layer and outer core layer are formed from conventional thermoset rubber-based compositions 3 and 1, respectively of TABLE VII above. As shown in TABLE VII, core formulations 1, 2 and 3 differ from each other by at least one of the amount of peroxide, the amount of zinc diacrylate, and presence/absence of an antioxidant.

TABLE VIII below incorporates the details of TABLE VI and TABLE VII therein and further specifies the construction and certain additional properties for each of golf balls Ex. 9, Ex. 10, and Comp. Ex. 3:

TABLE VIII Golf Ball Construction EXAMPLES & Properties Ex. 9 Ex. 10 Comp. Ex. 3 Inner Core TP_(p)(1) TP_(p)(2) Core Material Formulation 3³¹ Inner Core 0.75 0.50 1.00 Diameter (in.) Center Hardness 38.9 45.8 71.0 (Shore C) Inner Core ≦40 ≦40 >40 Compression Outer Core Core Core Core Material Formulation Formulation Formulation 2 1 1 Outer Core 0.400 0.525 0.275 Thickness (in.) Outer Core Surf. 89.1 87.2 87.5 Hardness (Shore C) Dual Core 65 98 88 Compression Intermediate Surlyn ® Surlyn ® Surlyn ® Layer Material 7940/8940³² 7940/8940 7940/8940 Intermediate 0.035 0.035 0.035 Layer Thickness (in.) Intermediate 69.2 69.1 69.3 Layer Hardness (Shore D) Cover Material MDI³³/ MDI MDI PTMEG³⁴/ PTMEG PTMEG E-300³⁵ E-300 E-300 Cover Thickness 0.030 0.030 0.030 (in.) Cover Hardness 82.8 82.5 82.1 (Shore C) Ball 83 102 99 Compression ³¹Core Formulations 1, 2 & 3 herein as set forth in TABLE VII above. ³²Surlyn ®7940 (Li) and Surlyn ®8940 (Na), are medium acid, monovalent and medium flow ionomers. ³³Methylene diphenyl diisocyanate. ³⁴Polytetramethylene ether glycol. ³⁵Ethacure 300, dimethylthiotoluene diamine, sold by Albemarle.

Referring to golf balls Ex. 9 and Ex. 10 of TABLE VIII, each dual core comprises a very soft, low compression inner core layer surrounded by a hard higher compression outer core layer. Additionally, each inner core layer has a diameter of less than 1.10 inches, is formed from a plasticized thermoplastic composition, and has a center Shore C hardness of 50 or less.

Meanwhile, each outer core layer has a thickness of 0.200 inches or greater, is formed from a thermosetting rubber composition, and has an outer surface Shore C hardness of 70 or greater. Finally, in each of the dual cores of golf balls Ex. 9 and Ex. 10, the outer core layer has an outer surface hardness that is at least 40 Shore C points greater than the center hardness of the inner core layer.

Specifically referring to golf ball Ex. 9, the plasticized thermoplastic inner core layer has a diameter of 0.75 in., and has a center Shore C hardness of 38.9. The thermoset rubber outer core layer meanwhile has a thickness of 0.400 in., is formed from core formulation TP₂(1), and has an outer surface Shore C hardness of 89.1. The outer surface hardness of the outer core layer of golf ball Ex. 9 is therefore “at least 40 Shore C points greater than the center hardness of the inner core layer” (namely 52.2 Shore C points greater than the center hardness). Interestingly, golf ball Ex. 9 also satisfies the embodiment wherein the center Shore C hardness is 40 or less, the outer surface Shore C hardness is 75 or greater, and the outer surface hardness is at least 50 Shore C points greater than the center hardness.

Notably, in golf ball Ex. 10, TP_(p)(2) differs from TP_(p)(1) of golf ball Ex. 9 in the choice of ionomer resin and fatty acid ester. Several property differences may also be noted between golf balls Ex. 10 and Ex. 9, respectively: inner core layer center Shore C hardnesses (45.8 versus 38.9); outer core layer surface Shore C hardnesses (87.2 versus 89.1); dual core compressions (89 versus 76); intermediate layer Shore D hardnesses (69.1 versus 69.2); cover layer surface shore C hardness (82.5 versus 82.8); and golf ball compression (102 versus 83). Nevertheless, golf ball Ex. 10 has an outer core layer outer surface hardness that is greater than the center hardness of the inner core layer by 41.4 Shore C hardness points, above “at least 40 Shore C points greater” of one embodiment of a golf ball of the invention. Property differences between golf balls Ex. 10 and Ex. 9 may be attributed to the outer core layer formulation differences between TP_(p)(2) and TP_(p)(1) as well to the above-identified inner core formulation differences.

Comparative golf ball Comp. Ex. 3, unlike golf balls Ex. 9 and Ex. 10, incorporates conventional thermoset rubber-based compositions in both the inner core layer and an outer core layer. The inner core layer of Comp. Ex. 3 is formed from a conventional thermoset rubber-based composition having a center Shore C hardness well above 50 (namely 71). Meanwhile, the outer core layer of Comp. Ex. 3 has an outer surface Shore C hardness that is not “at least 40 Shore C points greater than the center hardness of the inner core layer” but rather, well below that, namely only 16.5 Shore C points greater.

Accordingly, each of golf balls Ex. 9 and Ex. 10, incorporates a core having a steep positive Shore C hardness gradient progressing from a hard core outer surface to a very soft center, whereas the core of golf ball Comp. Ex. 3 has a center Shore C hardness above 50 and a much more shallow Shore C hardness gradient from outer surface to center and well below “at least 40”.

Inner Core Layer Plasticized Thermoplastic Compositions

In general, the thermoplastic composition used to form the inner core of golf balls such as those depicted in TABLE VIII may comprise: a) an acid copolymer of ethylene and an α,β-unsaturated carboxylic acid, optionally including a softening monomer selected from the group consisting of alkyl acrylates and methacrylates; and b) a plasticizer. A cation source may be present in an amount sufficient to neutralize from about 0% to about 100% of all acid groups present in the composition. In one preferred embodiment, the cation source is present in an amount sufficient to neutralize greater than 20% of all acid groups present in the composition. In one embodiment, the thermoplastic composition comprises a fatty acid salt.

The composition may comprise a highly-neutralized polymer (HNP); partially-neutralized acid polymer; or lowly-neutralized or non-neutralized acid polymer, and blends thereof as described further below. Suitable plasticizers that may be used to plasticize the thermoplastic compositions are also described further below. The thermoplastic composition may further comprise a non-acid polymer and optional additives and fillers. Suitable non-acid polymers include, for example, polyolefins, polyamides, polyesters, polyethers, polyurethanes, metallocene-catalyzed polymers, single-site catalyst polymerized polymers, ethylene propylene rubber, ethylene propylene diene rubber, styrenic block copolymer rubbers, alkyl acrylate rubbers, and functionalized derivatives thereof.

Various plasticizers may be used in the compositions of the inner core. For example, the thermoplastic composition may comprise a fatty acid ester, particularly an alkyl oleate, and more particularly ethyl oleate. The thermoplastic composition may comprise about 3 to about 50% by weight plasticizer, more preferably about 8 to about 42%, and even more preferably about 10 to about 30%, plasticizer based on weight of composition.

Suitable HNP compositions, which will be plasticized per this invention, comprise an HNP and optionally melt-flow modifier(s), additive(s), and/or filler(s). For purposes of the present disclosure, “HNP” refers to an acid polymer after at least 70%, preferably at least 80%, more preferably at least 90%, more preferably at least 95%, and even more preferably 100%, of the acid groups present are neutralized. It is understood that the HNP may be a blend of two or more HNPs. Preferred acid polymers are copolymers of an α-olefin and a C₃-C₈ α,β-ethylenically unsaturated carboxylic acid, optionally including a softening monomer. The α-olefin is preferably selected from ethylene and propylene. The acid is preferably selected from (meth)acrylic acid, ethacrylic acid, maleic acid, crotonic acid, fumaric acid, and itaconic acid. (Meth)acrylic acid is particularly preferred. The optional softening monomer is preferably selected from alkyl(meth)acrylate, wherein the alkyl groups have from 1 to 8 carbon atoms. Preferred acid polymers include, but are not limited to, those wherein the α-olefin is ethylene, the acid is (meth)acrylic acid, and the optional softening monomer is selected from (meth)acrylate, n-butyl (meth)acrylate, isobutyl(meth)acrylate, methyl (meth)acrylate, and ethyl (meth)acrylate. Particularly preferred acid polymers include, but are not limited to, ethylene/(meth)acrylic acid/n-butyl acrylate, ethylene/(meth)acrylic acid/methyl acrylate, and ethylene/(meth)acrylic acid/ethyl acrylate.

Suitable acid polymers for forming the HNP also include acid polymers that are already partially neutralized. Examples of suitable partially neutralized acid polymers include, but are not limited to, Surlyn® ionomers, commercially available from E. I. du Pont de Nemours and Company; AClyn® ionomers, commercially available from Honeywell International Inc.; and Iotek® ionomers, commercially available from ExxonMobil Chemical Company. Also suitable are DuPont® HPF 1000 and DuPont® HPF 2000, ionomeric materials commercially available from E. I. du Pont de Nemours and Company. In some embodiments, very low modulus ionomer-(“VLMI-”) type ethylene-acid polymers are particularly suitable for forming the HNP, such as Surlyn® 6320, Surlyn® 8120, Surlyn® 8320, and Surlyn® 9320, commercially available from E. I. du Pont de Nemours and Company.

The α-olefin is typically present in the acid polymer in an amount of 15 wt % or greater, or 25 wt % or greater, or 40 wt % or greater, or 60 wt % or greater, based on the total weight of the acid polymer. The acid is typically present in the acid polymer in an amount within a range having a lower limit of 1 or 2 or 4 or 6 or 8 or 10 or 12 or 15 or 16 or 20 wt % and an upper limit of 20 or 25 or 26 or 30 or 35 or 40 wt %, based on the total weight of the acid polymer. The optional softening monomer is typically present in the acid polymer in an amount within a range having a lower limit of 0 or 1 or 3 or 5 or 11 or 15 or 20 wt % and an upper limit of 23 or 25 or 30 or 35 or 50 wt %, based on the total weight of the acid polymer.

Additional suitable acid polymers are more fully described, for example, in U.S. Pat. Nos. 5,691,418, 6,562,906, 6,653,382, 6,777,472, 6,762,246, 6,815,480, and 6,953,820 and U.S. Patent Application Publication Nos. 2005/0148725, 2005/0049367, 2005/0020741, 2004/0220343, and 2003/0130434, the entire disclosures of which are hereby incorporated herein by reference.

The HNP is formed by reacting the acid polymer with a sufficient amount of cation source, optionally in the presence of a high molecular weight organic acid or salt thereof, such that at least 70%, preferably at least 80%, more preferably at least 90%, more preferably at least 95%, and even more preferably 100%, of all acid groups present are neutralized. The resulting HNP composition is plasticized with a plasticizer. Suitable plasticizers are described further below. In a particular embodiment, the cation source is present in an amount sufficient to neutralize, theoretically, greater than 100%, or 105% or greater, or 110% or greater, or 115% or greater, or 120% or greater, or 125% or greater, or 200% or greater, or 250% or greater of all acid groups present in the composition. The acid polymer can be reacted with the optional high molecular weight organic acid or salt thereof and the cation source simultaneously, or the acid polymer can be reacted with the optional high molecular weight organic acid or salt thereof prior to the addition of the cation source.

Suitable cation sources include metal ions and compounds of alkali metals, alkaline earth metals, and transition metals; metal ions and compounds of rare earth elements; and combinations thereof. Preferred cation sources are metal ions and compounds of magnesium, sodium, potassium, cesium, calcium, barium, manganese, copper, zinc, tin, lithium, and rare earth metals. The acid polymer may be at least partially neutralized prior to contacting the acid polymer with the cation source to form the HNP. Methods of preparing ionomers, and the acid polymers on which ionomers are based, are disclosed, for example, in U.S. Pat. Nos. 3,264,272, and 4,351,931, and U.S. Patent Application Publication No. 2002/0013413.

Suitable high molecular weight organic acids, for both the metal salt and as a component of the ester plasticizer, are aliphatic organic acids, aromatic organic acids, saturated monofunctional organic acids, unsaturated monofunctional organic acids, multi-unsaturated monofunctional organic acids, and dimerized derivatives thereof. Particular examples of suitable organic acids include, but are not limited to, caproic acid, caprylic acid, capric acid, lauric acid, stearic acid, behenic acid, erucic acid, oleic acid, linoleic acid, myristic acid, benzoic acid, palmitic acid, phenylacetic acid, naphthalenoic acid, dimerized derivatives thereof, and combinations thereof. Salts of high molecular weight organic acids comprise the salts, particularly the barium, lithium, sodium, zinc, bismuth, chromium, cobalt, copper, potassium, strontium, titanium, tungsten, magnesium, and calcium salts, of aliphatic organic acids, aromatic organic acids, saturated monofunctional organic acids, unsaturated monofunctional organic acids, multi-unsaturated monofunctional organic acids, dimerized derivatives thereof, and combinations thereof. Suitable organic acids and salts thereof are more fully described, for example, in U.S. Pat. No. 6,756,436, the entire disclosure of which is hereby incorporated herein by reference. In a particular embodiment, the HNP composition comprises an organic acid salt in an amount of 20 phr or greater, or 25 phr or greater, or 30 phr or greater, or 35 phr or greater, or 40 phr or greater.

The plasticized HNP compositions of the present invention optionally contain one or more melt-flow modifiers. The amount of melt-flow modifier in the composition is readily determined such that the melt-flow index of the composition is at least 0.1 g/10 min, preferably from 0.5 g/10 min to 10.0 g/10 min, and more preferably from 1.0 g/10 min to 6.0 g/10 min, as measured using ASTM D-1238, condition E, at 190° C., using a 2160 gram weight.

It is not required that a conventional melt-flow modifier be added to the plasticized HNP composition of this invention. Such melt-flow modifiers are optional. If a melt-flow modifier is added, it may be selected from the group of traditional melt-flow modifiers including, but not limited to, the high molecular weight organic acids and salts thereof disclosed above, polyamides, polyesters, polyacrylates, polyurethanes, polyethers, polyureas, polyhydric alcohols, and combinations thereof. Also suitable are the non-fatty acid melt-flow modifiers disclosed in U.S. Pat. Nos. 7,365,128 and 7,402,629, the entire disclosures of which are hereby incorporated herein by reference. However, as discussed above, certain plasticizers are added to the composition of this invention, and it is recognized that such plasticizers may modify the melt-flow of the composition in some instances.

The plasticized HNP compositions of the present invention optionally include additive(s) and/or filler(s) in an amount within a range having a lower limit of 0 or 5 or 10 wt %, and an upper limit of 15 or 20 or 25 or 30 or 50 wt %, based on the total weight of the composition. Suitable additives and fillers include, but are not limited to, chemical blowing and foaming agents, optical brighteners, coloring agents, fluorescent agents, whitening agents, UV absorbers, light stabilizers, defoaming agents, processing aids, mica, talc, nano-fillers, antioxidants, stabilizers, softening agents, fragrance components, impact modifiers, TiO₂, acid copolymer wax, surfactants, and fillers, such as zinc oxide, tin oxide, barium sulfate, zinc sulfate, calcium oxide, calcium carbonate, zinc carbonate, barium carbonate, clay, tungsten, tungsten carbide, silica, lead silicate, regrind (recycled material), and mixtures thereof. Suitable additives are more fully disclosed, for example, in U.S. Patent Application Publication No. 2003/0225197, the entire disclosure of which is hereby incorporated herein by reference.

In some embodiments, the plasticized HNP composition is a “moisture resistant” HNP composition, i.e., having a moisture vapor transmission rate (“MVTR”) of 8 g-mil/100 in²/day or less (i.e., 3.2 g-mm/m²·day or less), or 5 g-mil/100 in²/day or less (i.e., 2.0 g-mm/m²·day or less), or 3 g-mil/100 in²/day or less (i.e., 1.2 g-mm/m²·day or less), or 2 g-mil/100 in²/day or less (i.e., 0.8 g-mm/m²·day or less), or 1 g-mil/100 in²/day or less (i.e., 0.4 g-mm/m²·day or less), or less than 1 g-mil/100 in²/day (i.e., less than 0.4 g-mm/m²·day). Suitable moisture resistant HNP compositions are disclosed, for example, in U.S. Patent Application Publication Nos. 2005/0267240, 2006/0106175, and 2006/0293464, the entire disclosures of which are hereby incorporated herein by reference.

The plasticized HNP compositions of the present invention are not limited by any particular method or any particular equipment for making the compositions. In a preferred embodiment, the composition is prepared by the following process. The acid polymer(s), plasticizers, optional melt-flow modifier(s), and optional additive(s)/filler(s) are simultaneously or individually fed into a melt extruder, such as a single or twin screw extruder. Other suitable methods for incorporating the plasticizer into the composition are described further below. A suitable amount of cation source is then added such that at least 70%, or at least 80%, or at least 90%, or at least 95%, or at least 100%, of all acid groups present are neutralized. Optionally, the cation source is added in an amount sufficient to neutralize, theoretically, 105% or greater, or 110% or greater, or 115% or greater, or 120% or greater, or 125% or greater, or 200% or greater, or 250% or greater of all acid groups present in the composition. The acid polymer may be at least partially neutralized prior to the above process. The components are intensively mixed prior to being extruded as a strand from the die-head.

The HNP composition, which will be plasticized with specific plasticizers as described in detail below, optionally comprises at least one additional polymer component selected from partially neutralized ionomers as disclosed, for example, in U.S. Patent Application Publication No. 2006/0128904, the entire disclosure of which is hereby incorporated herein by reference; bimodal ionomers, such as those disclosed in U.S. Patent Application Publication No. 2004/0220343 and U.S. Pat. Nos. 6,562,906, 6,762,246, 7,273,903, 8,193,283, 8,410,219, and 8,410,220, the entire disclosures of which are hereby incorporated herein by reference, and particularly Surlyn® AD 1043, 1092, and 1022 ionomer resins, commercially available from E. I. du Pont de Nemours and Company; ionomers modified with rosins, such as those disclosed in U.S. Patent Application Publication No. 2005/0020741, the entire disclosure of which is hereby incorporated by reference; soft and resilient ethylene copolymers, such as those disclosed U.S. Patent Application Publication No. 2003/0114565, the entire disclosure of which is hereby incorporated herein by reference; polyolefins, such as linear, branched, or cyclic, C₂-C₄₀ olefins, particularly polymers comprising ethylene or propylene copolymerized with one or more C₂-C₄₀ olefins, C₃-C₂₀α-olefins, or C₃-C₁₀ α-olefins; polyamides; polyesters; polyethers; polycarbonates; polysulfones; polyacetals; polylactones; acrylonitrile-butadiene-styrene resins; polyphenylene oxide; polyphenylene sulfide; styrene-acrylonitrile resins; styrene maleic anhydride; polyimides; aromatic polyketones; ionomers and ionomeric precursors, acid copolymers, and conventional HNPs, such as those disclosed in U.S. Pat. Nos. 6,756,436, 6,894,098, and 6,953,820, the entire disclosures of which are hereby incorporated herein by reference; polyurethanes; grafted and non-grafted metallocene-catalyzed polymers, such as single-site catalyst polymerized polymers, high crystalline acid polymers, cationic ionomers, and combinations thereof.

Other polymer components that may be included in the plasticized HNP composition include, for example, natural and synthetic rubbers, including, but not limited to, ethylene propylene rubber (“EPR”), ethylene propylene diene rubber (“EPDM”), styrenic block copolymer rubbers (such as SI, SIS, SB, SBS, SIBS, and the like, where “S” is styrene, “I” is isobutylene, and “B” is butadiene), butyl rubber, halobutyl rubber, copolymers of isobutylene and para-alkylstyrene, halogenated copolymers of isobutylene and para-alkylstyrene, natural rubber, polyisoprene, copolymers of butadiene with acrylonitrile, polychloroprene, alkyl acrylate rubber (such as ethylene-alkyl acrylates and ethylene-alkyl methacrylates, and, more specifically, ethylene-ethyl acrylate, ethylene-methyl acrylate, and ethylene-butyl acrylate), chlorinated isoprene rubber, acrylonitrile chlorinated isoprene rubber, and polybutadiene rubber (cis and trans). Additional suitable blend polymers include those described in U.S. Pat. No. 5,981,658, for example at column 14, lines 30 to 56, the entire disclosure of which is hereby incorporated herein by reference.

The blend may be produced by post-reactor blending, by connecting reactors in series to make reactor blends, or by using more than one catalyst in the same reactor to produce multiple species of polymer. The polymers may be mixed prior to being put into an extruder, or they may be mixed in an extruder. In a particular embodiment, the plasticized HNP composition comprises an acid copolymer and an additional polymer component, wherein the additional polymer component is a non-acid polymer present in an amount of greater than 50 wt %, or an amount within a range having a lower limit of 50 or 55 or 60 or 65 or 70 and an upper limit of 80 or 85 or 90, based on the combined weight of the acid copolymer and the non-acid polymer. In another particular embodiment, the plasticized HNP composition comprises an acid copolymer and an additional polymer component, wherein the additional polymer component is a non-acid polymer present in an amount of less than 50 wt %, or an amount within a range having a lower limit of 10 or 15 or 20 or 25 or 30 and an upper limit of 40 or 45 or 50, based on the combined weight of the acid copolymer and the non-acid polymer.

The plasticized HNP compositions of the present invention, in the neat (i.e., unfilled) form, preferably have a specific gravity of from 0.95 g/cc to 0.99 g/cc. Any suitable filler, flake, fiber, particle, or the like, of an organic or inorganic material may be added to the HNP composition to increase or decrease the specific gravity, particularly to adjust the weight distribution within the golf ball, as further disclosed in U.S. Pat. Nos. 6,494,795, 6,547,677, 6,743,123, 7,074,137, and 6,688,991, the entire disclosures of which are hereby incorporated herein by reference.

In a particular embodiment, the plasticized HNP composition is selected from the relatively “soft” HNP compositions disclosed in U.S. Pat. No. 7,468,006, the entire disclosure of which is hereby incorporated herein by reference, and the low modulus HNP compositions disclosed in U.S. Pat. No. 7,207,903, the entire disclosure of which is hereby incorporated herein by reference. In a particular aspect of this embodiment, a sphere formed from the HNP composition has a compression of 80 or less, or 70 or less, or 65 or less, or 60 or less, or 50 or less, or 40 or less, or 30 or less, or 20 or less. In another particular aspect of this embodiment, the plasticized HNP composition has a material hardness within a range having a lower limit of 40 or 50 or 55 Shore C and an upper limit of 70 or 80 or 87 Shore C, or a material hardness of 55 Shore D or less, or a material hardness within a range having a lower limit of 10 or 20 or 30 or 37 or 39 or 40 or 45 Shore D and an upper limit of 48 or 50 or 52 or 55 or 60 or 80 Shore D. In yet another particular aspect of this embodiment, the plasticized HNP composition comprises an HNP having a modulus within a range having a lower limit of 1,000 or 5,000 or 10,000 psi and an upper limit of 17,000 or 25,000 or 28,000 or 30,000 or 35,000 or 45,000 or 50,000 or 55,000 psi, as measured using a standard flex bar according to ASTM D790-B.

In another particular embodiment, the plasticized HNP composition is selected from the relatively “hard” HNP compositions disclosed in U.S. Pat. No. 7,468,006, the entire disclosure of which is hereby incorporated herein by reference, and the high modulus HNP compositions disclosed in U.S. Pat. No. 7,207,903, the entire disclosure of which is hereby incorporated herein by reference. In a particular aspect of this embodiment, a sphere formed from the plasticized HNP composition has a compression of 70 or greater, or 80 or greater, or a compression within a range having a lower limit of 70 or 80 or 90 or 100 and an upper limit of 110 or 130 or 140. In another particular aspect of this embodiment, the HNP composition has a material hardness of 35 Shore D or greater, or 45 Shore D or greater, or a material hardness within a range having a lower limit of 45 or 50 or 55 or 57 or 58 or 60 or 65 or 70 or 75 Shore D and an upper limit of 75 or 80 or 85 or 90 or 95 Shore D. In yet another particular aspect of this embodiment, the plasticized HNP composition comprises an HNP having a modulus within a range having a lower limit of 25,000 or 27,000 or 30,000 or 40,000 or 45,000 or 50,000 or 55,000 or 60,000 psi and an upper limit of 72,000 or 75,000 or 100,000 or 150,000 psi, as measured using a standard flex bar according to ASTM D790-B. Suitable HNP compositions are further disclosed, for example, in U.S. Pat. Nos. 6,653,382, 6,756,436, 6,777,472, 6,815,480, 6,894,098, 6,919,393, 6,953,820, 6,994,638, 7,375,151, the entire disclosures of which are hereby incorporated herein by reference. Plasticizers, as described further below, are added to the above-described soft and hard and other HNP compositions.

In a particular embodiment, the HNP composition is formed by blending an acid polymer, a non-acid polymer, a cation source, and a fatty acid or metal salt thereof. The resulting HNP composition is plasticized with a plasticizer as described further below. For purposes of the present invention, maleic anhydride modified polymers are defined herein as a non-acid polymer despite having anhydride groups that can ring-open to the acid form during processing of the polymer to form the HNP compositions herein. The maleic anhydride groups are grafted onto a polymer, are present at relatively very low levels, and are not part of the polymer backbone, as is the case with the acid polymers, which are exclusively E/X and E/X/Y copolymers of ethylene and an acid, particularly methacrylic acid and acrylic acid.

In a particular aspect of this embodiment, the acid polymer is selected from ethylene-acrylic acid and ethylene-methacrylic acid copolymers, optionally containing a softening monomer selected from n-butyl acrylate, iso-butyl acrylate, and methyl acrylate. The acid polymer preferably has an acid content with a range having a lower limit of 2 or 10 or 15 or 16 weight % and an upper limit of 20 or 25 or 26 or 30 weight %. Examples of particularly suitable commercially available acid polymers include, but are not limited to, those given in TABLE IX below.

TABLE IX Acid Copolymers and Properties. Melt Index Softening (2.16 kg, Acid Monomer 190° C., Acid Polymer (wt %) (wt %) g/10 min) Nucrel ® 9-1 methacrylic n-butyl 25 acid (9.0) acrylate (23.5) Nucrel ® 599 methacrylic None 450 acid (10.0) Nucrel ® 960 methyacrylic None 60 acid (15.0) Nucrel ® 0407 methacrylic None 7.5 acid (4.0) Nucrel ® 0609 methacrylic None 9 acid (6.0) Nucrel ® 1214 methacrylic None 13.5 acid (12.0) Nucrel ® 2906 methacrylic None 60 acid (19.0) Nucrel ® 2940 methacrylic None 395 acid (19.0) Nucrel ® 30707 acrylic None 7 acid (7.0) Nucrel ® 31001 acrylic None 1.3 acid (9.5) Nucrel ® AE methacrylic isobutyl 11 acid (2.0) acrylate (6.0) Nucrel ® 2806 acrylic None 60 acid (18.0) Nucrel ® 0403 methacrylic None 3 acid (4.0) Nucrel ® 925 methacrylic None 25 acid (15.0) Escor ® AT-310 acrylic methyl 6 acid (6.5) acrylate (6.5) Escor ® AT-325 acrylic methyl 20 acid (6.0) acrylate (20.0) Escor ® AT-320 acrylic methyl 5 acid (6.0) acrylate (18.0) Escor ® 5070 acrylic None 30 acid (9.0) Escor ® 5100 acrylic None 8.5 acid (11.0) Escor ® 5200 acrylic None 38 acid (15.0) A-C ® 5120 acrylic None not acid (15) reported A-C ® 540 acrylic None not acid (5) reported A-C ® 580 acrylic None not acid (10) reported Primacor ® 3150 acrylic None 5.8 acid (6.5) Primacor ® 3330 acrylic None 11 acid (3.0) Primacor ® 5985 acrylic None 240 acid (20.5) Primacor ® 5986 acrylic None 300 acid (20.5) Primacor ® 5980I acrylic none 300 acid (20.5) Primacor ® 5990I acrylic none 1300 acid (20.0) XUS 60751.17 acrylic none 600 acid (19.8) XUS 60753.02L acrylic none 60 acid (17.0)

The non-acid polymer is preferably selected from the group consisting of polyolefins, polyamides, polyesters, polyethers, polyurethanes, metallocene-catalyzed polymers, single-site catalyst polymerized polymers, ethylene propylene rubber, ethylene propylene diene rubber, styrenic block copolymer rubbers, alkyl acrylate rubbers, and functionalized derivatives thereof.

In another particular aspect of this embodiment, the non-acid polymer is an elastomeric polymer. Suitable elastomeric polymers include, but are not limited to:

(a) ethylene-alkyl acrylate polymers, particularly polyethylene-butyl acrylate, polyethylene-methyl acrylate, and polyethylene-ethyl acrylate;

(b) metallocene-catalyzed polymers;

(c) ethylene-butyl acrylate-carbon monoxide polymers and ethylene-vinyl acetate-carbon monoxide polymers;

(d) polyethylene-vinyl acetates;

(e) ethylene-alkyl acrylate polymers containing a cure site monomer;

(f) ethylene-propylene rubbers and ethylene-propylene-diene monomer rubbers;

(g) olefinic ethylene elastomers, particularly ethylene-octene polymers, ethylene-butene polymers, ethylene-propylene polymers, and ethylene-hexene polymers;

(h) styrenic block copolymers;

(i) polyester elastomers;

(j) polyamide elastomers;

(k) polyolefin rubbers, particularly polybutadiene, polyisoprene, and styrene-butadiene rubber; and

(l) thermoplastic polyurethanes.

Examples of particularly suitable commercially available non-acid polymers include, but are not limited to, Lotader® ethylene-alkyl acrylate polymers and Lotryl® ethylene-alkyl acrylate polymers, and particularly Lotader® 4210, 4603, 4700, 4720, 6200, 8200, and AX8900 commercially available from Arkema Corporation; Elvaloy® AC ethylene-alkyl acrylate polymers, and particularly AC 1224, AC 1335, AC 2116, AC3117, AC3427, and AC34035, commercially available from E. I. du Pont de Nemours and Company; Fusabond® elastomeric polymers, such as ethylene vinyl acetates, polyethylenes, metallocene-catalyzed polyethylenes, ethylene propylene rubbers, and polypropylenes, and particularly Fusabond® N525, C190, C250, A560, N416, N493, N614, P614, M603, E100, E158, E226, E265, E528, and E589, commercially available from E. I. du Pont de Nemours and Company; Honeywell A-C polyethylenes and ethylene maleic anhydride copolymers, and particularly A-C 5180, A-C 575, A-C 573, A-C 655, and A-C 395, commercially available from Honeywell; Nordel® IP rubber, Elite® polyethylenes, Engage® elastomers, and Amplify® functional polymers, and particularly Amplify® GR 207, GR 208, GR 209, GR 213, GR 216, GR 320, GR 380, and EA 100, commercially available from The Dow Chemical Company; Enable® metallocene polyethylenes, Exact® plastomers, Vistamaxx® propylene-based elastomers, and Vistalon® EPDM rubber, commercially available from ExxonMobil Chemical Company; Starflex® metallocene linear low density polyethylene, commercially available from LyondellBasell; Elvaloy® HP4051, HP441, HP661 and HP662 ethylene-butyl acrylate-carbon monoxide polymers and Elvaloy® 741, 742 and 4924 ethylene-vinyl acetate-carbon monoxide polymers, commercially available from E. I. du Pont de Nemours and Company; Evatane® ethylene-vinyl acetate polymers having a vinyl acetate content of from 18 to 42%, commercially available from Arkema Corporation; Elvax® ethylene-vinyl acetate polymers having a vinyl acetate content of from 7.5 to 40%, commercially available from E. I. du Pont de Nemours and Company; Vamac® G terpolymer of ethylene, methylacrylate and a cure site monomer, commercially available from E. I. du Pont de Nemours and Company; Vistalon® EPDM rubbers, commercially available from ExxonMobil Chemical Company; Kraton® styrenic block copolymers, and particularly Kraton® FG1901GT, FG1924GT, and RP6670GT, commercially available from Kraton Performance Polymers Inc.; Septon® styrenic block copolymers, commercially available from Kuraray Co., Ltd.; Hytrel® polyester elastomers, and particularly Hytrel® 3078, 4069, and 556, commercially available from E. I. du Pont de Nemours and Company; Riteflex® polyester elastomers, commercially available from Celanese Corporation; Pebax® thermoplastic polyether block amides, and particularly Pebax® 2533, 3533, 4033, and 5533, commercially available from Arkema Inc.; Affinity® and Affinity® GA elastomers, Versify® ethylene-propylene copolymer elastomers, and Infuse® olefin block copolymers, commercially available from The Dow Chemical Company; Exxelor® polymer resins, and particularly Exxelor® PE 1040, PO 1015, PO 1020, VA 1202, VA 1801, VA 1803, and VA 1840, commercially available from ExxonMobil Chemical Company; and Royaltuf® EPDM, and particularly Royaltuf®498 maleic anhydride modified polyolefin based on an amorphous EPDM and Royaltuf®485 maleic anhydride modified polyolefin based on an semi-crystalline EPDM, commercially available from Chemtura Corporation.

Additional examples of particularly suitable commercially available elastomeric polymers include, but are not limited to, those given in TABLE X below.

TABLE X Non-Acid Elastomeric Polymers and Properties. Melt Index (2.16 kg, % Maleic 190° C., % Ester Anhydride g/10 min) Polyethylene Butyl Acrylates Lotader ® 3210 6 3.1 5 Lotader ® 4210 6.5 3.6 9 Lotader ® 3410 17 3.1 5 Lotryl ® 17BA04 16-19 0 3.5-4.5 Lotryl ® 35BA320 33-37 0 260-350 Elvaloy ® AC 3117 17 0 1.5 Elvaloy ® AC 3427 27 0 4 Elvaloy ® AC 34035 35 0 40 Polyethylene Methyl Acrylates Lotader ® 4503 19 0.3 8 Lotader ® 4603 26 0.3 8 Lotader ® AX 8900 26 8% GMA 6 Lotryl ® 24MA02 23-26 0 1-3 Elvaloy ® AC 12024S 24 0 20 Elvaloy ® AC 1330 30 0 3 Elvaloy ® AC 1335 35 0 3 Elvaloy ® AC 1224 24 0 2 Polyethylene Ethyl Acrylates Lotader ® 6200 6.5 2.8 40 Lotader ® 8200 6.5 2.8 200 Lotader ® LX 4110 5 3.0 5 Lotader ® HX 8290 17 2.8 70 Lotader ® 5500 20 2.8 20 Lotader ® 4700 29 1.3 7 Lotader ® 4720 29 0.3 7 Elvaloy ® AC 2116 16 0 1

In the plasticized HNP compositions, the acid polymer and non-acid polymer are combined and reacted with a cation source, such that at least 80% of all acid groups present are neutralized. The resulting plasticized HNP composition also includes a plasticizer as described further below. The present invention is not meant to be limited by a particular order for combining and reacting the acid polymer, non-acid polymer and cation source. In a particular embodiment, the fatty acid or metal salt thereof is used in an amount such that the fatty acid or metal salt thereof is present in the HNP composition in an amount of from 10 wt % to 60 wt %, or within a range having a lower limit of 10 or 20 or 30 or 40 wt % and an upper limit of 40 or 50 or 60 wt %, based on the total weight of the HNP composition. Suitable cation sources and fatty acids and metal salts thereof are further disclosed above.

In another particular aspect of this embodiment, the acid polymer is an ethylene-acrylic acid polymer having an acid content of 19 wt % or greater, the non-acid polymer is a metallocene-catalyzed ethylene-butene copolymer, optionally modified with maleic anhydride, the cation source is magnesium, and the fatty acid or metal salt thereof is magnesium oleate present in the composition in an amount of 20 to 50 wt %, based on the total weight of the composition. This preferred HNP composition is treated with a plasticizer as described further below.

As discussed above, the ethylene acid copolymer may be blended with other materials including, but not limited to, partially- and fully-neutralized ionomers optionally blended with a maleic anhydride-grafted non-ionomeric polymer, graft copolymers of ionomer and polyamide, and the following non-ionomeric polymers, including homopolymers and copolymers thereof, as well as their derivatives that are compatibilized with at least one grafted or copolymerized functional group, such as maleic anhydride, amine, epoxy, isocyanate, hydroxyl, sulfonate, phosphonate, and the like. Other suitable materials that may be blended with the ethylene acid copolymer include, for example the following polymers (including homopolymers, copolymers, and derivatives thereof):

-   -   (a) polyesters, particularly those modified with a         compatibilizing group such as sulfonate or phosphonate,         including modified poly(ethylene terephthalate), modified         poly(butylene terephthalate), modified poly(propylene         terephthalate), modified poly(trimethylene terephthalate),         modified poly(ethylene naphthenate), and those disclosed in U.S.         Pat. Nos. 6,353,050, 6,274,298, and 6,001,930, the entire         disclosures of which are hereby incorporated herein by         reference, and blends of two or more thereof;     -   (b) polyamides, polyamide-ethers, and polyamide-esters, and         those disclosed in U.S. Pat. Nos. 6,187,864, 6,001,930, and         5,981,654, the entire disclosures of which are hereby         incorporated herein by reference, and blends of two or more         thereof;     -   (c) polyurethanes, polyureas, polyurethane-polyurea hybrids, and         blends of two or more thereof;     -   (d) fluoropolymers, such as those disclosed in U.S. Pat. Nos.         5,691,066, 6,747,110 and 7,009,002, the entire disclosures of         which are hereby incorporated herein by reference, and blends of         two or more thereof;     -   (e) non-ionomeric acid polymers, such as E/X- and E/X/Y-type         polymers, wherein E is an olefin (e.g., ethylene), X is a         carboxylic acid such as acrylic, methacrylic, crotonic, maleic,         fumaric, or itaconic acid, and Y is a softening comonomer such         as vinyl esters of aliphatic carboxylic acids wherein the acid         has from 2 to 10 carbons, alkyl ethers wherein the alkyl group         has from 1 to 10 carbons, and alkyl alkylacrylates such as alkyl         methacrylates wherein the alkyl group has from 1 to 10 carbons;         and blends of two or more thereof;     -   (f) metallocene-catalyzed polymers, such as those disclosed in         U.S. Pat. Nos. 6,274,669, 5,919,862, 5,981,654, and 5,703,166,         the entire disclosures of which are hereby incorporated herein         by reference, and blends of two or more thereof;     -   (g) polystyrenes, such as poly(styrene-co-maleic anhydride),         acrylonitrile-butadiene-styrene, poly(styrene sulfonate),         polyethylene styrene, and blends of two or more thereof;     -   (h) polypropylenes and polyethylenes, particularly grafted         polypropylene and grafted polyethylenes that are modified with a         functional group, such as maleic anhydride of sulfonate, and         blends of two or more thereof;     -   (i) polyvinyl chlorides and grafted polyvinyl chlorides, and         blends of two or more thereof;     -   (j) polyvinyl acetates, preferably having less than about 9% of         vinyl acetate by weight, and blends of two or more thereof;     -   (k) polycarbonates, blends of         polycarbonate/acrylonitrile-butadiene-styrene, blends of         polycarbonate/polyurethane, blends of polycarbonate/polyester,         and blends of two or more thereof;     -   (l) polyvinyl alcohols, and blends of two or more thereof;     -   (m) polyethers, such as polyarylene ethers, polyphenylene         oxides, block copolymers of alkenyl aromatics with vinyl         aromatics and poly(amic ester)s, and blends of two or more         thereof;     -   (n) polyimides, polyetherketones, polyamideimides, and blends of         two or more thereof;     -   (o) polycarbonate/polyester copolymers and blends; and     -   (p) combinations of any two or more of the above thermoplastic         polymers.

Suitable ionomeric compositions comprise one or more acid polymers, each of which is partially- or fully-neutralized, and optionally additives, fillers, and/or melt-flow modifiers. Suitable acid polymers are salts of homopolymers and copolymers of α,β-ethylenically unsaturated mono- or dicarboxylic acids, and combinations thereof, optionally including a softening monomer, and preferably having an acid content (prior to neutralization) of from 1 wt % to 30 wt %, more preferably from 5 wt % to 20 wt %. The acid polymer is preferably neutralized to 70% or higher, including up to 100%, with a suitable cation source, such as metal cations and salts thereof, organic amine compounds, ammonium, and combinations thereof. Preferred cation sources are metal cations and salts thereof, wherein the metal is preferably lithium, sodium, potassium, magnesium, calcium, barium, lead, tin, zinc, aluminum, manganese, nickel, chromium, copper, or a combination thereof.

Suitable additives and fillers include, for example, blowing and foaming agents, optical brighteners, coloring agents, fluorescent agents, whitening agents, UV absorbers, light stabilizers, defoaming agents, processing aids, mica, talc, nanofillers, antioxidants, stabilizers, softening agents, fragrance components, impact modifiers, acid copolymer wax, surfactants; inorganic fillers, such as zinc oxide, titanium dioxide, tin oxide, calcium oxide, magnesium oxide, barium sulfate, zinc sulfate, calcium carbonate, zinc carbonate, barium carbonate, mica, talc, clay, silica, lead silicate, and the like; high specific gravity metal powder fillers, such as tungsten powder, molybdenum powder, and the like; regrind, i.e., core material that is ground and recycled; and nano-fillers. Suitable melt-flow modifiers include, for example, fatty acids and salts thereof, polyamides, polyesters, polyacrylates, polyurethanes, polyethers, polyureas, polyhydric alcohols, and combinations thereof.

Suitable ionomeric compositions include blends of highly neutralized polymers (i.e., neutralized to 70% or higher) with partially neutralized ionomers as disclosed, for example, in U.S. Patent Application Publication No. 2006/0128904, the entire disclosure of which is hereby incorporated herein by reference. Suitable ionomeric compositions also include blends of one or more partially- or fully-neutralized polymers with additional thermoplastic and thermoset materials, including, but not limited to, non-ionomeric acid copolymers, engineering thermoplastics, fatty acid/salt-based highly neutralized polymers, polybutadienes, polyurethanes, polyureas, polyesters, polycarbonate/polyester blends, thermoplastic elastomers, maleic anhydride-grafted metallocene-catalyzed polymers, and other conventional polymeric materials. Suitable ionomeric compositions are further disclosed, for example, in U.S. Pat. Nos. 6,653,382, 6,756,436, 6,777,472, 6,894,098, 6,919,393, and 6,953,820, the entire disclosures of which are hereby incorporated herein by reference.

Examples of commercially available thermoplastics suitable for forming core layers of golf balls disclosed herein include, but are not limited to, Pebax® thermoplastic polyether block amides, commercially available from Arkema Inc.; Surlyn® ionomer resins, Hytrel® thermoplastic polyester elastomers, and ionomeric materials sold under the trade names DuPont® HPF 1000 and HPF 2000, HPF AD 1035, HPF AD 1035 Soft, HPF AD 1040, all of which are commercially available from E. I. du Pont de Nemours and Company; Iotek® ionomers, commercially available from ExxonMobil Chemical Company; Amplify®IO ionomers of ethylene acrylic acid copolymers, commercially available from The Dow Chemical Company; Clarix® ionomer resins, commercially available from A. Schulman Inc.; Elastollan® polyurethane-based thermoplastic elastomers, commercially available from BASF; and Xylex® polycarbonate/polyester blends, commercially available from SABIC Innovative Plastics.

The thermoplastic compositions, which are described further below as being suitable for making cover layers, are also suitable for forming the core and cover layers of the golf balls herein, once the compositions are plasticized per this invention.

In a particular embodiment, the plasticized thermoplastic core or cover composition comprises a material selected from the group consisting of partially- and fully-neutralized ionomers optionally blended with a maleic anhydride-grafted non-ionomeric polymer, polyesters, polyamides, polyethers, and blends of two or more thereof and plasticizer.

In another particular embodiment, the plasticized thermoplastic core or cover composition is a blend of two or more ionomers and plasticizer. In a particular aspect of this embodiment, the thermoplastic composition is a 50 wt %/50 wt % blend of two different partially-neutralized ethylene/methacrylic acid polymers.

In another particular embodiment, the plasticized thermoplastic core or cover composition is a blend of one or more ionomers and a maleic anhydride-grafted non-ionomeric polymer and plasticizer. In a particular aspect of this embodiment, the non-ionomeric polymer is a metallocene-catalyzed polymer. In another particular aspect of this embodiment, the ionomer is a partially-neutralized ethylene/methacrylic acid polymer and the non-ionomeric polymer is a maleic anhydride-grafted metallocene-catalyzed polymer. In another particular aspect of this embodiment, the ionomer is a partially-neutralized ethylene/methacrylic acid polymer and the non-ionomeric polymer is a maleic anhydride-grafted metallocene-catalyzed polyethylene.

The plasticized thermoplastic core layer is optionally treated or admixed with a thermoset diene composition to reduce or prevent flow upon overmolding. Optional treatments may also include the addition of peroxide to the material prior to molding, or a post-molding treatment with, for example, a crosslinking solution, electron beam, gamma radiation, isocyanate or amine solution treatment, or the like. Such treatments may prevent the intermediate layer from melting and flowing or “leaking” out at the mold equator, as the thermoset outer core layer is molded thereon at a temperature necessary to crosslink the outer core layer, which is typically from 280° F. to 360° F. for a period of about 5 to 30 minutes.

Suitable thermoplastic core compositions, which are plasticized in accordance with the present invention, are further disclosed, for example, in U.S. Pat. Nos. 5,919,100, 6,872,774 and 7,074,137, the entire disclosures of which are hereby incorporated herein by reference.

As discussed above, in one preferred embodiment, at least 70% of the acid groups in the acid copolymer are neutralized, and these materials are referred to as HNP materials herein. However, it is understood that other acid copolymer compositions may be used in accordance with the present invention. For example, acid copolymer compositions having acid groups that are neutralized from about 20% to about less than 70% may be used, and these materials may be referred to as partially-neutralized ionomers. For example, the partially-neutralized ionomers may have a neutralization level of about 30% to about 65%, and more particularly about 35% to 60%.

Preferred ionomers are salts of O/X- and O/X/Y-type acid copolymers, wherein O is an α-olefin, X is a C₃-C₈ α,β-ethylenically unsaturated carboxylic acid, and Y is a softening monomer. O is preferably selected from ethylene and propylene. X is preferably selected from methacrylic acid, acrylic acid, ethacrylic acid, crotonic acid, and itaconic acid. Methacrylic acid and acrylic acid are particularly preferred. Y is preferably selected from (meth)acrylate and alkyl(meth)acrylates wherein the alkyl groups have from 1 to 8 carbon atoms, including, but not limited to, n-butyl (meth)acrylate, isobutyl(meth)acrylate, methyl (meth)acrylate, and ethyl (meth)acrylate.

Preferred O/X and O/X/Y-type copolymers include, without limitation, ethylene acid copolymers, such as ethylene/(meth)acrylic acid, ethylene/(meth)acrylic acid/maleic anhydride, ethylene/(meth)acrylic acid/maleic acid mono-ester, ethylene/maleic acid, ethylene/maleic acid mono-ester, ethylene/(meth)acrylic acid/n-butyl (meth)acrylate, ethylene/(meth)acrylic acid/iso-butyl(meth)acrylate, ethylene/(meth)acrylic acid/methyl (meth)acrylate, ethylene/(meth)acrylic acid/ethyl (meth)acrylate terpolymers, and the like. The term, “copolymer,” as used herein, includes polymers having two types of monomers, those having three types of monomers, and those having more than three types of monomers. Preferred α,β-ethylenically unsaturated mono- or dicarboxylic acids are (meth)acrylic acid, ethacrylic acid, maleic acid, crotonic acid, fumaric acid, itaconic acid. (Meth)acrylic acid is most preferred. As used herein, “(meth)acrylic acid” means methacrylic acid and/or acrylic acid. Likewise, “(meth)acrylate” means methacrylate and/or acrylate.

The O/X or O/X/Y-type copolymer is at least partially neutralized with a cation source. Suitable cation sources include, but are not limited to, metal ion sources, such as compounds of alkali metals, alkaline earth metals, transition metals, and rare earth elements; ammonium salts and monoamine salts; and combinations thereof. Preferred cation sources are compounds of magnesium, sodium, potassium, cesium, calcium, barium, manganese, copper, zinc, lead, tin, aluminum, nickel, chromium, lithium, and rare earth metals.

Also, as discussed above, it is recognized that the cation source is optional, and non-neutralized or lowly-neutralized compositions may be used. For example, acid copolymers having 0% to less than 20% neutralization levels may be used. Acid copolymer compositions containing plasticizers and having zero percent of the acid groups neutralized may be used per this invention. Also, acid copolymer ionomer compositions containing plasticizers, wherein 1 to 19% of the acid groups are neutralized, may be used. Particularly, acid copolymers having about about 3% to about 18% and more particularly about 6% to about 15% neutralization levels may be used in accordance with this invention.

It is also recognized that acid copolymer blends may be prepared including, but not limited to, acid copolymer compositions formed from: i) blends of two or more partially-neutralized ionomers; ii) blends of two or more highly-neutralized ionomers; iii) blends of two or more non-neutralized acid copolymers and/or lowly-neutralized ionomers; iv) blends of one or more highly-neutralized ionomers with one or more partially-neutralized ionomers, and/or lowly-neutralized ionomers, and/or non-neutralized acid copolymers; v) blends of partially-neutralized ionomers with one or more highly-neutralized ionomers, and/or lowly-neutralized ionomers, and/or non-neutralized acid copolymers.

(i) Exemplary Plasticizers for Making a Plasticized Thermoplastic Composition TP_(p) of the Inner Core

As discussed above, the ethylene acid copolymer compositions of this invention contain a plasticizer. Adding the plasticizers helps to reduce the glass transition temperature (Tg) of the composition. The glass transition in a polymer is a temperature range below which a polymer is relatively brittle and above which it is rubber-like. In addition to lowering the Tg, the plasticizer may also reduce the tan δ in the temperature range above the Tg. The Tg of a polymer is measured by a Differential Scanning Calorimeter or a Dynamic Mechanical Analyzer (DMA) and the DMA is used to measure tan δ. The plasticizer may also reduce the hardness and compression of the composition when compared to its non-plasticized condition. The effects of adding a plasticizer to the ethylene acid copolymer composition on Tg, flex modulus, hardness, and other physical properties are discussed further below.

The ethylene acid copolymer compositions may contain one or more plasticizers. The plasticizers that may be used in the ethylene acid copolymer compositions of this invention include, for example, N-butylbenzenesulfonamide (BBSA); N-ethylbenzenesulfonamide (EBSA); N-propylbenzenesulfonamide (PBSA); N-butyl-N-dodecylbenzenesulfonamide (BDBSA); N,N-dimethylbenzenesulfonamide (DMBSA); p-methylbenzenesulfonamide; o,p-toluene sulfonamide; p-toluene sulfonamide; 2-ethylhexyl-4-hydroxybenzoate; hexadecyl-4-hydroxybenzoate; 1-butyl-4-hydroxybenzoate; dioctyl phthalate; diisodecyl phthalate; di-(2-ethylhexyl) adipate; and tri-(2-ethylhexyl)phosphate.

In one preferred version, the plasticizer is selected from the group of polytetramethylene ether glycol (available from BASF under the tradename, PolyTHF™ 250); propylene carbonate (available from Huntsman Corp., under the tradename, Jeffsol™ PC); and/or dipropyleneglycol dibenzoate (available from Eastman Chemical under the tradename, Benzoflex™ 284). Mixtures of these plasticizers also may be used.

Other suitable plasticizer compounds include benzene mono-, di-, and tricarboxylic acid esters. Phthalates such as Bis(2-ethylhexyl) phthalate (DEHP), Diisononyl phthalate (DINP), Di-n-butyl phthalate (DnBP, DBP), Butyl benzyl phthalate (BBP), Diisodecyl phthalate (DIDP), Dioctyl phthalate (DnOP), Diisooctyl phthalate (DIOP), Diethyl phthalate (DEP), Diisobutyl phthalate (DIBP), and Di-n-hexyl phthalate are suitable. Iso- and terephthalates such as Dioctyl terephthalate and Dinonyl isophthalate may be used. Also appropriate are trimellitates such as Trimethyl trimellitate (TMTM), Tri-(2-ethylhexyl)trimellitate (TOTM), Tri-(n-octyl,n-decyl)trimellitate, Tri-(heptyl,nonyl)trimellitate, Tri-n-octyl trimellitate; as well as benzoates, including: 2-ethylhexyl-4-hydroxy benzoate, n-octyl benzoate, methyl benzoate, and ethyl benzoate.

Also suitable are alkyl diacid esters commonly based on C4-C12 alkyl dicarboxylic acids such as adipic, sebacic, azelaic, and maleic acids such as: Bis(2-ethylhexyl)adipate (DEHA), Dimethyl adipate (DMAD), Monomethyl adipate (MMAD), Dioctyl adipate (DOA), Dibutyl sebacate (DBS), Dibutyl maleate (DBM), Diisobutyl maleate (DIBM), Dioctyl sebacate (DOS). Also, esters based on glycols, polyglycols and polyhydric alcohols such as poly(ethylene glycol) mono- and di-esters, cyclohexanedimethanol esters, sorbitol derivatives; and triethylene glycol dihexanoate, diethylene glycol di-2-ethylhexanoate, tetraethylene glycol diheptanoate, and ethylene glycol dioleate may be used.

Fatty acids, fatty acid salts, fatty acid amides, and fatty acid esters also may be used in the compositions of this invention. Compounds such as stearic, oleic, ricinoleic, behenic, myristic, linoleic, palmitic, and lauric acid esters, salts, and mono- and bis-amides can be used. Ethyl oleate, butyl stearate, methyl acetylricinoleate, zinc oleate, ethylene bis-oleamide, and stearyl erucamide are suitable. Suitable fatty acid salts include, for example, metal stearates, erucates, laurates, oleates, palmitates, pelargonates, and the like. For example, fatty acid salts such as zinc stearate, calcium stearate, magnesium stearate, barium stearate, and the like can be used. Fatty alcohols and acetylated fatty alcohols are also suitable, as are carbonate esters such as propylene carbonate and ethylene carbonate. In a particularly preferred version, the fatty acid ester, ethyl oleate is used as the plasticizer.

Glycerol-based esters such as soy-bean, tung, or linseed oils or their epoxidized derivatives can also be used as plasticizers in the present invention, as can polymeric polyester plasticizers formed from the esterification reaction of diacids and diglycols as well as from the ring-opening polymerization reaction of caprolactones with diacids or diglycols. Citrate esters and acetylated citrate esters are also suitable. Glycerol mono-, di-, and tri-oleates may be used per this invention, and in one preferred embodiment, glycerol trioleate is used as the plasticizer.

Dicarboxylic acid molecules containing both a carboxylic acid ester and a carboxylic acid salt can perform suitably as plasticizers. The magnesium salt of mono-methyl adipate and the zinc salt of mono-octyl glutarate are two such examples for this invention. Tri- and tetra-carboxylic acid esters and salts can also be used.

Also envisioned as suitable plasticizers are organophosphate and organosulfur compounds such as tricresyl phosphate (TCP), tributyl phosphate (TBP), alkyl sulfonic acid phenyl esters (ASE); and sulfonamides such as N-ethyl toluene sulfonamide, N-(2-hydroxypropyl)benzene sulfonamide, N-(n-butyl)benzene sulfonamide. Furthermore, thioester and thioether variants of the plasticizer compounds mentioned above are suitable.

Non-ester plasticizers such as alcohols, polyhydric alcohols, glycols, polyglycols, and polyethers also are suitable materials for plasticization. Materials such as polytetramethylene ether glycol, poly(ethylene glycol), and poly(propylene glycol), oleyl alchohol, and cetyl alcohol can be used. Hydrocarbon compounds, both saturated and unsaturated, linear or cyclic can be used such as mineral oils, microcrystalline waxes, or low-molecular weight polybutadiene. Halogenated hydrocarbon compounds can also be used.

Other examples of plasticizers that may be used in the ethylene acid copolymer composition of this invention include butylbenzenesulphonamide (BBSA), ethylhexyl para-hydroxybenzoate (EHPB) and decylhexyl para-hydroxybenzoate (DHPB), as disclosed in Montanari et al., U.S. Pat. No. 6,376,037, the disclosure of which is hereby incorporated by reference.

Esters and alkylamides such as phthalic acid esters including dimethyl phthalate, diethyl phthalate, dibutyl phthalate, diheptyl phthalate, di-2-ethylhexyl phthalate, di-n-octyl phthalate, diisodecyl phthalate, ditridecyl phthalate, dicyclohexyl phthalate, butylbenzyl phthalate, diisononyl phthalate, ethylphthalylethyl glycolate, butylphthalylbutyl glycolate, diundecyl phthalate, di-2-ethylhexyl tetrahydrophthalate as disclosed in Isobe et al., U.S. Pat. No. 6,538,099, the disclosure of which is hereby incorporated by reference, also may be used.

Jacques et al., U.S. Pat. No. 7,045,185, the disclosure of which is hereby incorporated by reference, discloses sulphonamides such as N-butylbenzenesulphonamide, ethyltoluene-suiphonamide, N-cyclohexyltoluenesulphonamide, 2-ethylhexyl-para-hydroxybenzoate, 2-decylhexyl-para-hydroxybenzoate, oligoethyleneoxytetrahydrofurfuryl alcohol, or oligoethyleneoxy malonate; esters of hydroxybenzoic acid; esters or ethers of tetrahydrofurfuryl alcohol, and esters of citric acid or hydroxymalonic acid; and these plasticizers also may be used.

Sulfonamides also may be used in the present invention, and these materials are described in Fish, Jr. et al., U.S. Pat. No. 7,297,737, the disclosure of which is hereby incorporated by reference. Examples of such sulfonamides include N-alkyl benzenesulfonamides and toluenesufonamides, particularly N-butylbenzenesulfonamide, N-(2-hydroxypropyl)benzenesulfonamide, N-ethyl-o-toluenesulfonamide, N-ethyl-p-toluenesulfonamide, o-toluenesulfonamide, p-toluenesulfonamide. Such sulfonamide plasticizers also are described in Hochstetter et al., US Patent Application Publication 2010/0183837, the disclosure of which is hereby incorporated by reference.

As noted above, the fatty acid esters are particularly preferred plasticizers in the present invention. It has been found that the fatty acid esters perform well as plasticizers in the ethylene acid copolymer composition. The fatty acid esters have several advantageous properties. For example, the fatty acid esters are compatible with the ethylene acid copolymers and they tend to blend uniformly and completely with the acid copolymer. Also, the fatty acid esters tend to improve the resiliency and/or compression of the composition as discussed further below. The ethylene acid copolymer/plasticizer compositions may contain other ingredients that do not materially affect the basic and novel characteristics of the composition. For example, mineral fillers may be added as discussed above. In one particular version, the composition consists essentially of ethylene acid copolymer and plasticizer, particularly a fatty acid ester. In another particular version, the composition consists essentially of ethylene acid copolymer, cation source sufficient to neutralize at least 20% of the acid groups present in the composition, and plasticizer, particularly a fatty acid ester.

One method of preparing the fatty acid ester involves reacting the fatty acid or mixture of fatty acids with a corresponding alcohol. The alcohol can be any alcohol including, but not limited to, linear, branched, and cyclic alcohols. The fatty acid ester is commonly a methyl, ethyl, n-propyl, or butyl ester of a carboxylic acid that contains from 4 to 30 carbon atoms. In the present invention, ethyl esters and particularly ethyl oleate are preferred fatty acid esters because of their properties. The carboxylic acid may be saturated or unsaturated. Examples of suitable saturated carboxylic acids, that is, carboxylic acids in which the carbon atoms of the alkyl chain are connected by single bonds, include but are not limited to butyric acid (chain length of C₄ and molecular weight of 88.1); capric acid (C₁₀ and MW of 172.3); lauric acid (C₁₂ and MW of 200.3); myristic acid (C₁₄ and MW of 228.4); palmitic acid (C₁₆ and MW of 256.4); stearic acid (C₁₈ and MW of 284.5); and behenic acid (C₂₂ and MW of 340.6). Examples of suitable unsaturated carboxylic acids, that is, a carboxylic acid in which there is one or more double bonds between the carbon atoms in the alkyl chain, include but are not limited to oleic acid (chain length and unsaturation C18:1; and MW of 282.5); linoleic acid (C18:2 and MW of 280.5; linolenic acid (C18:3 and MW of 278.4); and erucic acid (C22:1 and MW of 338.6).

It is believed that the plasticizer should be added in a sufficient amount to the ethylene acid copolymer composition so there is a substantial change in the stiffness and/or hardness of the ethylene acid copolymer. Thus, although the concentration of plasticizer may be as little as 1% by weight to form some ethylene acid copolymer compositions per this invention, it is preferred that the concentration be relatively greater. For example, it is preferred that the concentration of the plasticizer be at least 3 weight percent (wt. %). More particularly, it is preferred that the plasticizer be present in an amount within a range having a lower limit of 1% or 3% or 5% or 7% or 8% or 10% or 12% or 15% or 18% and an upper limit of 20% or 22% or 25% or 30% or 35% or 40% or 42% or 50% or 55% or 60% or 66% or 71% or 75% or 80%. In one preferred embodiment, the concentration of plasticizer falls within the range of about 7% to about 75%, preferably about 9% to about 55%, and more preferably about 15% to about 50%.

It is believed that adding the plasticizer to the ethylene acid copolymer helps make the composition softer and more rubbery. Adding the plasticizers to the composition helps decrease the stiffness of the composition. That is, the plasticizer helps lower the flex modulus of the composition. The flex modulus refers to the ratio of stress to strain within the elastic limit (when measured in the flexural mode) and is similar to tensile modulus. This property is used to indicate the bending stiffness of a material. The flexural modulus, which is a modulus of elasticity, is determined by calculating the slope of the linear portion of the stress-strain curve during the bending test. If the slope of the stress-strain curve is relatively steep, the material has a relatively high flexural modulus meaning the material resists deformation. The material is more rigid. If the slope is relatively flat, the material has a relatively low flexural modulus meaning the material is more easily deformed. The material is more flexible. The flex modulus can be determined in accordance with ASTM D790 standard among other testing procedures. Thus, in one embodiment, the first ethylene acid copolymer (containing ethylene acid copolymer only) composition has a first flex modulus value and the second ethylene acid copolymer (containing ethylene acid copolymer and plasticizer) composition has a second flex modulus value, wherein the second flex modulus value is at least 1% less; or at least 2% less; or at least 4% less; or at least 8% less; or at least 10% less than the first modulus value.

Plasticized thermoplastic compositions of the present invention are not limited by any particular method or any particular equipment for making the compositions. In a preferred embodiment, the composition is prepared by the following process. The acid copolymer(s), plasticizer, optional melt-flow modifier(s), and optional additive(s)/filler(s) are simultaneously or individually fed into a melt extruder, such as a single or twin screw extruder. If the acid polymer is to be neutralized, a suitable amount of cation source is then added to achieve the desired level of neutralization neutralized. The acid polymer may be partially or fully neutralized prior to the above process. The components are intensively mixed prior to being extruded as a strand from the die-head. Additional methods for incorporating plasticizer into the thermoplastic compositions herein are disclosed in co-pending U.S. patent application Ser. No. 13/929,841, as well as in U.S. Pat. Nos. 8,523,708 and 8,523,709, which are fully incorporated by reference herein.

More particularly, in one embodiment, the ethylene acid copolymer/plasticizer composition has a flex modulus lower limit of about 500 (or less), 1,000, 1,600, 2,000, 4,200, 7,500, 9,000, 10,000 or 20,000 or 40,000 or 50,000 or 60,000 or 70,000 or 80,000 or 90,000 or 100,000; and a flex modulus upper limit of about 110,000 or 120,000 or 130,000 psi or 140,000 or 160,000 or 180,000 or 200,000 or 300,000 or greater. In general, the properties of flex modulus and hardness are related, whereby flex modulus measures the material's resistance to bending, and hardness measures the material's resistance to indentation. In general, as the flex modulus of the material increases, the hardness of the material also increases. As discussed above, adding the plasticizer to the ethylene acid copolymer helps reduce the flex modulus of the composition and it also helps reduce hardness to a certain degree. Thus, in one embodiment, the ethylene acid copolymer/plasticizer composition is relatively soft and having a hardness of no greater than 40 Shore D or no greater than 55 Shore C. For example, the Shore D hardness may be within a range having a lower limit of 5 or 8 or 10 or 12 or 14 and an upper limit of 28 or 30 or 32 or 34 or 35 or 38 or 40 Shore D. The Shore C hardness may be within the range having a lower limit of 10 or 13 or 15 or 17 or 19 and an upper limit of 44 or 46 or 48 or 50 or 53 or 55 Shore C. In other embodiments, the ethylene acid copolymer/plasticizer composition is moderately soft having a hardness of no greater than about 60 Shore D or no greater than 75 Shore C. For example, the Shore D hardness may be within a range having a lower limit of 25, 28, 20, 32, 35, 36, 38, or 40, and an upper limit of 42, 45, 48, 50, 54, 56, or 60. The Shore C hardness may be within the range of having a lower limit of 30, 33, 35, 37, 39, 41, or 43, and an upper limit of 62, 64, 66, 68, 71, 73 or 75 Shore C. In yet other embodiments, the ethylene acid copolymer/plasticizer composition is moderately hard having a hardness no greater than 95 Shore D or no greater than 99 C. For example, the Shore D hardness may be within the range having a lower limit of about 42, 44, 47, 51, 53, or 58 and an upper limit of about 60, 65, 72, 77, 80, 84, 91, or 95 Shore D. The Shore C hardness may be within the range having a lower limit of 57, 59, 62, 66, or 72 and an upper limit of about 75, 78, 84, 87, 90, 93, 95, 97, or 99 Shore C.

It also is believed that adding the plasticizer to the ethylene acid copolymer composition helps reduce the glass transition temperature (Tg) of the composition in many instances. Thus, in one embodiment, the first ethylene acid copolymer (containing ethylene acid copolymer only) composition has a first Tg value and the second ethylene acid copolymer (containing ethylene acid copolymer and plasticizer) composition has a second Tg value, wherein the second Tg value is at least 1 degree (1°) less; or at least 2° less; or at least 4° less; or at least 8°; or at least 10° less than the first Tg value. In other embodiments, the first Tg value and the second Tg value are approximately the same.

In addition, introducing the specific plasticizers of this invention into the ethylene acid copolymer composition generally helps to reduce the compression and/or increase the COR of the composition (when molded into a solid sphere and tested) versus a non-plasticized composition (when molded into a solid sphere and tested.) Plasticized ethylene acid copolymer compositions typically show compression values lower, or at most equal to, non-plasticized compositions while the plasticized compositions display COR values that may be higher, or at the least equal to, non-plasticized compositions. This effect is surprising, because in many conventional compositions, the compression of the composition increases as the COR increases. In some instances plasticization of the composition might produce a slight reduction in the COR while at the same time reducing the compression to a greater extent, thereby providing an overall improvement to the compression/COR relationship over the non-plasticized composition. In this regard, TABLES XI through XIII below provide such comparisons for HPF, Surlyn and Nucrel compositions, respectively.

TABLE XI HPF Compositions Solid Sphere Solid Sphere Solid Sphere Solid Sphere Shore D Shore C Example COR Compression Hardness Hardness HPF AD1035³⁶ 0.822 63 41.7 70.0 HPF AD1035 0.782 35 35.6 59.6 Soft³⁷ HPF 2000³⁸ 0.856 91 46.1 76.5 HPF 2000 with 0.839 68 37.9 68.8 10% EO³⁹ HPF 2000 with 0.810 32 30.2 53.0 20% EO HPF 2000 with 0.768 −12 22.7 39.4 30% EO ³⁶HPF AD1035—acid copolymer ionomer resin, available from the DuPont Company. ³⁷HPF AD1035 Soft—acid copolymer ionomer resin, available from the DuPont Company. ³⁸HPF 2000—acid copolymer ionomer resin, available from the DuPont Company. ³⁹EO—ethyl oleate (plasticizer)

TABLE XII Surlyn 9320 Compositions Solid Sphere Solid Sphere Solid Sphere Solid Sphere Shore D Shore C Example COR Compression Hardness Hardness Surlyn 0.559 40 37.2 62.1 9320⁴⁰ Surlyn 0.620 6 26.3 45.8 9320 with 10% EO Surlyn 0.618 −31 24.9 38.4 9320 with 20% EO Surlyn 0.595 −79 18.7 28.0 9320 with 30% EO ⁴⁰Surlyn 9320 is based on a copolymer of ethylene with 23.5% n-butyl acrylate and about 9% methacrylic acid that is about 41% neutralized with a zinc cation source, available from the DuPont Company.

TABLE XIII Nucrel 9-1 Compositions Solid Sphere Solid Sphere Solid Sphere Solid Sphere Shore D Shore C Example COR Compression Hardness Hardness Nucrel 9-1⁴¹ 0.449 −37 23.2 40.3 Nucrel 9-1 with 0.501 −67 19.1 26.3 10% EO ⁴¹Nucrel 9-1: is a copolymer of ethylene with 23.5% n-butyl acrylate, and about 9% methacrylic acid that is non-neutralized, available from the DuPont Company. Outer Core Layer

Meanwhile, the outer core layer of golf balls such as those depicted in TABLE VIII may be formed from any non-plasticized thermoplastic composition or any thermosetting composition disclosed herein or otherwise known in the art. For example, it is envisioned that the outer core layer in golf balls of the invention may incorporate thermoplastic and/or thermoset compositions such as shown in TABLE II and TABLE V as well as TABLE VIII. In this regard, examples Ex. 9 and Ex. 10 of TABLE VIII above incorporate an outer core layer formed from a thermosetting composition, which should not be construed as limiting the invention.

Intermediate Layers and Cover Layers

The optional intermediate layer(s) of golf balls such as those depicted in TABLE VIII, whether disposed between the inner core layer and outer core layer, or disposed between the outer core layer and cover, are not limited by a particular composition for forming the layer(s), and can be formed from any suitable golf ball composition including, but not limited to, natural rubber; polybutadiene; polyisoprene; ethylene propylene rubber; ethylene-propylene-diene rubber; styrene-butadiene rubber; butyl rubber; halobutyl rubber; thermoset polyurethane; thermoset polyurea; acrylonitrile butadiene rubber; polychloroprene; alkyl acrylate rubber; chlorinated isoprene rubber; acrylonitrile chlorinated isoprene rubber; polyalkenamer rubber; polyester; polyacrylate; partially- and fully-neutralized ionomer; graft copolymer of ionomer and polyamide; polyester, particularly polyesters modified with a compatibilizing group such as sulfonate or phosphonate, including modified poly(ethylene terephthalate), modified poly(butylene terephthalate), modified poly(propylene terephthalate), modified poly(trimethylene terephthalate), modified poly(ethylene naphthenate), including, but not limited to, those disclosed in U.S. Pat. Nos. 6,353,050, 6,274,298, and 6,001,930, the entire disclosures of which are hereby incorporated herein by reference; polyamides, polyamide-ethers, and polyamide-esters, including, but not limited to, those disclosed in U.S. Pat. Nos. 6,187,864, 6,001,930, and 5,981,654, the entire disclosures of which are hereby incorporated herein by reference; polyurethanes, polyureas, and polyurethane-polyurea hybrids, including, but not limited to, those disclosed in U.S. Pat. Nos. 5,334,673, 5,484,870, 6,506,851, 6,756,436, 6,835,794, 6,867,279, 6,960,630, and 7,105,623, U.S. Patent Application Publication No. 2007/0117923, and U.S. Patent Application Ser. No. 60/401,047 and Ser. No. 13/613,095, the entire disclosures of which are hereby incorporated herein by reference; fluoropolymers, including, but not limited to, those disclosed in U.S. Pat. Nos. 5,691,066, 6,747,110 and 7,009,002, the entire disclosures of which are hereby incorporated herein by reference; non-ionomeric acid polymers, i.e., E/X- and E/X/Y-type copolymers, including, but not limited to, those disclosed in U.S. Pat. No. 6,872,774, the entire disclosure of which is hereby incorporated herein by reference; metallocene-catalyzed polymers, including, but not limited to, those disclosed in U.S. Pat. Nos. 6,274,669, 5,919,862, 5,981,654, and 5,703,166, the entire disclosures of which are hereby incorporated herein by reference; polystyrenes, such as poly(styrene-co-maleic anhydride), acrylonitrile-butadiene-styrene, poly(styrene sulfonate), polyethylene styrene; polypropylenes, polyethylenes, propylene elastomers, ethylene elastomers, and copolymers of propylene and ethylene; polyvinyl chlorides; polyvinyl acetates, preferably having less than about 9% of vinyl acetate by weight; polycarbonates, blends of polycarbonate/acrylonitrile-butadiene-styrene, blends of polycarbonate/polyurethane, and blends of polycarbonate/polyester; polyvinyl alcohols; polyethers, such as polyarylene ethers, polyphenylene oxides, and block copolymers of alkenyl aromatics with vinyl aromatics and poly(amic ester)s; polyimides, polyetherketones, and polyamideimides; polycarbonate/polyester copolymers; and combinations of two or more thereof.

Thermoplastic core compositions are optionally treated or admixed with a thermoset diene composition to reduce or prevent flow upon overmolding. Optional treatments may also include the addition of peroxide to the material prior to molding, or a post-molding treatment with, for example, a crosslinking solution, electron beam, gamma radiation, isocyanate or amine solution treatment, or the like. Such treatments may prevent the intermediate layer from melting and flowing or “leaking” out at the mold equator, as thermoset layers are molded thereon at a temperature necessary to crosslink the thermoset layer, which is typically from 280° F. to 360° F. for a period of about 5 to 30 minutes.

The multi-layer core is enclosed with a cover, which may be a single-, dual-, or multi-layer cover, preferably having an overall thickness within a range having a lower limit of 0.010 or 0.020 or 0.025 or 0.030 or 0.040 or 0.045 inches and an upper limit of 0.050 or 0.060 or 0.070 or 0.075 or 0.080 or 0.090 or 0.100 or 0.150 or 0.200 or 0.300 or 0.500 inches. In a particular embodiment, the cover is a single layer having a thickness of from 0.010 or 0.020 or 0.025 inches to 0.035 or 0.040 or 0.050 inches. In another particular embodiment, the cover consists of an inner cover layer having a thickness of from 0.010 or 0.020 or 0.025 inches to 0.035 or 0.050 inches and an outer cover layer having a thickness of from 0.010 or 0.020 or 0.025 inches to 0.035 or 0.040 inches.

Suitable cover materials include, but are not limited to, polyurethanes, polyureas, and hybrids of polyurethane and polyurea; ionomer resins and blends thereof (e.g., Surlyn® ionomer resins and DuPont® HPF 1000 and HPF 2000, commercially available from E. I. du Pont de Nemours and Company; Iotek® ionomers, commercially available from ExxonMobil Chemical Company; Amplify®IO ionomers of ethylene acrylic acid copolymers, commercially available from The Dow Chemical Company; and Clarix® ionomer resins, commercially available from A. Schulman Inc.); polyisoprene; polyoctenamer, such as Vestenamer® polyoctenamer, commercially available from Evonik Industries; polyethylene, including, for example, low density polyethylene, linear low density polyethylene, and high density polyethylene; polypropylene; rubber-toughened olefin polymers; non-ionomeric acid copolymers, e.g., (meth)acrylic acid, which do not become part of an ionomeric copolymer; plastomers; flexomers; styrene/butadiene/styrene block copolymers; styrene/ethylene-butylene/styrene block copolymers; polybutadiene; styrene butadiene rubber; ethylene propylene rubber; ethylene propylene diene rubber; dynamically vulcanized elastomers; ethylene vinyl acetates; ethylene(meth)acrylates; polyvinyl chloride resins; polyamides, amide-ester elastomers, and copolymers of ionomer and polyamide, including, for example, Pebax® thermoplastic polyether and polyester amides, commercially available from Arkema Inc; crosslinked trans-polyisoprene; polyester-based thermoplastic elastomers, such as Hytrel® polyester elastomers, commercially available from E. I. du Pont de Nemours and Company, and Riteflex® polyester elastomers, commercially available from Ticona; polyurethane-based thermoplastic elastomers, such as Elastollan® polyurethanes, commercially available from BASF; synthetic or natural vulcanized rubber; and combinations thereof.

Compositions comprising an ionomer or a blend of two or more ionomers are particularly suitable cover materials. Preferred ionomeric cover compositions include:

-   -   (a) a composition comprising a “high acid ionomer” (i.e., having         an acid content of greater than 16 wt %), such as Surlyn 8150®;     -   (b) a composition comprising a high acid ionomer and a maleic         anhydride-grafted non-ionomeric polymer (e.g., Fusabond®         functionalized polymers). A particularly preferred blend of high         acid ionomer and maleic anhydride-grafted polymer is a 84 wt         %/16 wt % blend of Surlyn 8150® and Fusabond®. Blends of high         acid ionomers with maleic anhydride-grafted polymers are further         disclosed, for example, in U.S. Pat. Nos. 6,992,135 and         6,677,401, the entire disclosures of which are hereby         incorporated herein by reference;     -   (c) a composition comprising a 50/45/5 blend of Surlyn®         8940/Surlyn® 9650/Nucrel® 960, preferably having a material         hardness of from 80 to 85 Shore C;     -   (d) a composition comprising a 50/25/25 blend of Surlyn®         8940/Surlyn® 9650/Surlyn® 9910, preferably having a material         hardness of about 90 Shore C;     -   (e) a composition comprising a 50/50 blend of Surlyn®         8940/Surlyn® 9650, preferably having a material hardness of         about 86 Shore C;     -   (f) a composition comprising a blend of Surlyn® 7940/Surlyn®         8940, optionally including a melt flow modifier;     -   (g) a composition comprising a blend of a first high acid         ionomer and a second high acid ionomer, wherein the first high         acid ionomer is neutralized with a different cation than the         second high acid ionomer (e.g., 50/50 blend of Surlyn® 8150 and         Surlyn® 9150), optionally including one or more melt flow         modifiers such as an ionomer, ethylene-acid copolymer or ester         terpolymer; and     -   (h) a composition comprising a blend of a first high acid         ionomer and a second high acid ionomer, wherein the first high         acid ionomer is neutralized with a different cation than the         second high acid ionomer, and from 0 to 10 wt % of an         ethylene/acid/ester ionomer wherein the ethylene/acid/ester         ionomer is neutralized with the same cation as either the first         high acid ionomer or the second high acid ionomer or a different         cation than the first and second high acid ionomers (e.g., a         blend of 40-50 wt % Surlyn® 8140, 40-50 wt % Surlyn® 9120, and         0-10 wt % Surlyn® 6320).

Surlyn 8150®, Surlyn® 8940, and Surlyn® 8140 are different grades of E/MAA copolymer in which the acid groups have been partially neutralized with sodium ions. Surlyn® 9650, Surlyn® 9910, Surlyn® 9150, and Surlyn® 9120 are different grades of E/MAA copolymer in which the acid groups have been partially neutralized with zinc ions. Surlyn® 7940 is an E/MAA copolymer in which the acid groups have been partially neutralized with lithium ions. Surlyn® 6320 is a very low modulus magnesium ionomer with a medium acid content. Nucrel® 960 is an E/MAA copolymer resin nominally made with 15 wt % methacrylic acid. Surlyn® ionomers, Fusabond® polymers, and Nucrel® copolymers are commercially available from E. I. du Pont de Nemours and Company.

Ionomeric cover compositions can be blended with non-ionic thermoplastic resins, particularly to manipulate product properties. Examples of suitable non-ionic thermoplastic resins include, but are not limited to, polyurethane, poly-ether-ester, poly-amide-ether, polyether-urea, thermoplastic polyether block amides (e.g., Pebax® block copolymers, commercially available from Arkema Inc.), styrene-butadiene-styrene block copolymers, styrene(ethylene-butylene)-styrene block copolymers, polyamides, polyesters, polyolefins (e.g., polyethylene, polypropylene, ethylene-propylene copolymers, polyethylene-(meth)acrylate, plyethylene-(meth)acrylic acid, functionalized polymers with maleic anhydride grafting, Fusabond® functionalized polymers commercially available from E. I. du Pont de Nemours and Company, functionalized polymers with epoxidation, elastomers (e.g., ethylene propylene diene monomer rubber, metallocene-catalyzed polyolefin) and ground powders of thermoset elastomers.

Ionomer golf ball cover compositions may include a flow modifier, such as, but not limited to, acid copolymer resins (e.g., Nucrel® acid copolymer resins, and particularly Nucrel® 960, commercially available from E. I. du Pont de Nemours and Company), performance additives (e.g., A-C® performance additives, particularly A-C® low molecular weight ionomers and copolymers, A-C® oxidized polyethylenes, and A-C® ethylene vinyl acetate waxes, commercially available from Honeywell International Inc.), fatty acid amides (e.g., ethylene bis-stearamide and ethylene bis-oleamide), fatty acids and salts thereof

Suitable ionomeric cover materials are further disclosed, for example, in U.S. Pat. Nos. 6,653,382, 6,756,436, 6,894,098, 6,919,393, and 6,953,820, the entire disclosures of which are hereby incorporated by reference.

Polyurethanes, polyureas, and blends and hybrids of polyurethane/polyurea are also particularly suitable for forming cover layers. Suitable polyurethanes and polyureas are further disclosed, for example, in U.S. Pat. Nos. 5,334,673, 5,484,870, 6,506,851, 6,756,436, 6,835,794, 6,867,279, 6,960,630, and 7,105,623; U.S. Patent Application Publication No. 2009/0011868; and U.S. Patent Application No. 60/401,047, the entire disclosures of which are hereby incorporated herein by reference. Suitable polyurethane-urea cover materials include polyurethane/polyurea blends and copolymers comprising urethane and urea segments, as disclosed in U.S. Patent Application Publication No. 2007/0117923, the entire disclosure of which is hereby incorporated herein by reference.

Cover compositions may include one or more filler(s), such as titanium dioxide, barium sulfate, etc., and/or additive(s), such as coloring agents, fluorescent agents, whitening agents, antioxidants, dispersants, UV absorbers, light stabilizers, plasticizers, surfactants, compatibility agents, foaming agents, reinforcing agents, release agents, and the like.

Suitable cover materials and constructions also include, but are not limited to, those disclosed in U.S. Patent Application Publication No. 2005/0164810, U.S. Pat. Nos. 5,919,100, 6,117,025, 6,767,940, and 6,960,630, and PCT Publications WO00/23519 and WO00/29129, the entire disclosures of which are hereby incorporated herein by reference.

In a particular embodiment, the cover is a single layer, preferably formed from an ionomeric composition having a material hardness of 60 Shore D or greater or a material hardness of from 60 or 62 or 65 Shore D to 65 or 70 or 72 Shore D, and a thickness of 0.02 inches or greater or 0.03 inches or greater or 0.04 inches or greater or a thickness within a range having a lower limit of 0.010 or 0.015 or 0.020 inches and an upper limit of 0.035 or 0.040 or 0.050 inches.

In another particular embodiment, the cover is a single layer having a thickness of from 0.010 or 0.025 inches to 0.035 or 0.040 inches and formed from a thermoplastic composition selected from ionomer-, polyurethane-, and polyurea-based compositions having a material hardness of 62 Shore D or less, or less than 62 Shore D, or 60 Shore D or less, or less than 60 Shore D, or 55 Shore D or less, or less than 55 Shore D.

In another particular embodiment, the cover is a single layer having a thickness of from 0.010 or 0.025 inches to 0.035 or 0.040 inches and formed from a thermosetting polyurethane- or polyurea-based composition having a material hardness of 62 Shore D or less, or less than 62 Shore D, or 60 Shore D or less, or less than 60 Shore D, or 55 Shore D or less, or less than 55 Shore D.

In another particular embodiment, the cover comprises an inner cover layer formed from an ionomeric composition and an outer cover layer formed from a thermosetting polyurethane- or polyurea-based composition. The inner cover layer composition preferably has a material hardness of from 60 or 62 or 65 Shore D to 65 or 70 or 72 Shore D. The inner cover layer preferably has a thickness within a range having a lower limit of 0.010 or 0.020 or 0.030 inches and an upper limit of 0.035 or 0.040 or 0.050 inches. The outer cover layer composition preferably has a material hardness of 62 Shore D or less, or less than 62 Shore D, or 60 Shore D or less, or less than 60 Shore D, or 55 Shore D or less, or less than 55 Shore D. The outer cover layer preferably has a thickness within a range having a lower limit of 0.010 or 0.020 or 0.025 inches and an upper limit of 0.035 or 0.040 or 0.050 inches.

In another particular embodiment, the cover comprises an inner cover layer formed from an ionomeric composition and an outer cover layer formed from a thermoplastic composition selected from ionomer-, polyurethane-, and polyurea-based compositions. The inner cover layer composition preferably has a material hardness of from 60 or 62 or 65 Shore D to 65 or 70 or 72 Shore D. The inner cover layer preferably has a thickness within a range having a lower limit of 0.010 or 0.020 or 0.030 inches and an upper limit of 0.035 or 0.040 or 0.050 inches. The outer cover layer composition preferably has a material hardness of 62 Shore D or less, or less than 62 Shore D, or 60 Shore D or less, or less than 60 Shore D, or 55 Shore D or less, or less than 55 Shore D. The outer cover layer preferably has a thickness within a range having a lower limit of 0.010 or 0.020 or 0.025 inches and an upper limit of 0.035 or 0.040 or 0.050 inches.

In another particular embodiment, the cover is a dual- or multi-layer cover including an inner or intermediate cover layer formed from an ionomeric composition and an outer cover layer formed from a polyurethane- or polyurea-based composition. The ionomeric layer preferably has a surface hardness of 70 Shore D or less, or 65 Shore D or less, or less than 65 Shore D, or a Shore D hardness of from 50 to 65, or a Shore D hardness of from 57 to 60, or a Shore D hardness of 58, and a thickness within a range having a lower limit of 0.010 or 0.020 or 0.030 inches and an upper limit of 0.045 or 0.080 or 0.120 inches. The outer cover layer is preferably formed from a castable or reaction injection moldable polyurethane, polyurea, or copolymer or hybrid of polyurethane/polyurea. Such cover material is preferably thermosetting, but may be thermoplastic. The outer cover layer composition preferably has a material hardness of 85 Shore C or less, or 45 Shore D or less, or 40 Shore D or less, or from 25 Shore D to 40 Shore D, or from 30 Shore D to 40 Shore D. The outer cover layer preferably has a surface hardness within a range having a lower limit of 20 or 30 or 35 or 40 Shore D and an upper limit of 52 or 58 or 60 or 65 or 70 or 72 or 75 Shore D. The outer cover layer preferably has a thickness within a range having a lower limit of 0.010 or 0.015 or 0.025 inches and an upper limit of 0.035 or 0.040 or 0.045 or 0.050 or 0.055 or 0.075 or 0.080 or 0.115 inches.

A moisture vapor barrier layer is optionally employed between the core and the cover. Moisture vapor barrier layers are further disclosed, for example, in U.S. Pat. Nos. 6,632,147, 6,838,028, 6,932,720, 7,004,854, and 7,182,702, and U.S. Patent Application Publication Nos. 2003/0069082, 2003/0069085, 2003/0130062, 2004/0147344, 2004/0185963, 2006/0068938, 2006/0128505 and 2007/0129172, the entire disclosures of which are hereby incorporated herein by reference.

Thermoplastic layers herein may be treated in such a manner as to create a positive or negative hardness gradient. In golf ball layers of the present invention wherein a thermosetting rubber is used, gradient-producing processes and/or gradient-producing rubber formulation may be employed. Gradient-producing processes and formulations are disclosed more fully, for example, in U.S. patent application Ser. No. 12/048,665, filed on Mar. 14, 2008; Ser. No. 11/829,461, filed on Jul. 27, 2007; Ser. No. 11/772,903, filed Jul. 3, 2007; Ser. No. 11/832,163, filed Aug. 1, 2007; Ser. No. 11/832,197, filed on Aug. 1, 2007; the entire disclosure of each of these references is hereby incorporated herein by reference.

Golf balls of the present invention will typically have dimple coverage of 60% or greater, preferably 65% or greater, and more preferably 75% or greater.

Additional Construction and Measurement Considerations

The United States Golf Association specifications limit the minimum size of a competition golf ball to 1.680 inches. There is no specification as to the maximum diameter, and golf balls of any size can be used for recreational play. Golf balls of the present invention can have an overall diameter of any size. The preferred diameter of the present golf balls is within a range having a lower limit of 1.680 inches and an upper limit of 1.740 or 1.760 or 1.780 or 1.800 inches.

Golf balls of the present invention preferably have a moment of inertia (“MOI”) of 70-95 g·cm², preferably 75-93 g·cm², and more preferably 76-90 g·cm². For low MOI embodiments, the golf ball preferably has an MOI of 85 g·cm² or less, or 83 g·cm² or less. For high MOI embodiment, the golf ball preferably has an MOI of 86 g·cm² or greater, or 87 g·cm² or greater. MOI is measured on a model MOI-005-104 Moment of Inertia Instrument manufactured by Inertia Dynamics of Collinsville, Conn. The instrument is connected to a PC for communication via a COMM port and is driven by MOI Instrument Software version #1.2.

For purposes of the present invention, “compression” refers to Atti compression and is measured according to a known procedure, using an Atti compression test device, wherein a piston is used to compress a ball against a spring. The travel of the piston is fixed and the deflection of the spring is measured. The measurement of the deflection of the spring does not begin with its contact with the ball; rather, there is an offset of approximately the first 1.25 mm (0.05 inches) of the spring's deflection. Very low compression cores will not cause the spring to deflect by more than 1.25 mm and therefore have a zero or negative compression measurement. The Atti compression tester is designed to measure objects having a diameter of 1.680 inches; thus, smaller objects, such as golf ball cores, must be shimmed to a total height of 1.680 inches to obtain an accurate reading. Conversion from Atti compression to Riehle (cores), Riehle (balls), 100 kg deflection, 130-10 kg deflection or effective modulus can be carried out according to the formulas given in Compression by Any Other Name, Science and Golf IV, Proceedings of the World Scientific Congress of Golf (Eric Thain ed., Routledge, 2002).

COR, as used herein, is determined according to a known procedure wherein a sphere is fired from an air cannon at two given velocities and calculated at a velocity of 125 ft/s. Ballistic light screens are located between the air cannon and the steel plate at a fixed distance to measure ball velocity. As the sphere travels toward the steel plate, it activates each light screen, and the time at each light screen is measured. This provides an incoming transit time period inversely proportional to the sphere's incoming velocity. The sphere impacts the steel plate and rebounds through the light screens, which again measures the time period required to transit between the light screens. This provides an outgoing transit time period inversely proportional to the sphere's outgoing velocity. COR is then calculated as the ratio of the outgoing transit time period to the incoming transit time period, COR=V_(out)/V_(in)=T_(in)/T_(out).

The surface hardness of a golf ball layer is obtained from the average of a number of measurements taken from opposing hemispheres, taking care to avoid making measurements on the parting line of the core or on surface defects, such as holes or protrusions. Hardness measurements are made pursuant to ASTM D-2240 using a calibrated, digital durometer, capable of reading to 0.1 hardness units and set to record the maximum hardness reading obtained for each measurement.

The center hardness of a core is obtained according to the following procedure. The core is gently pressed into a hemispherical holder having an internal diameter approximately slightly smaller than the diameter of the core, such that the core is held in place in the hemispherical portion of the holder while concurrently leaving the geometric central plane of the core exposed. The core is secured in the holder by friction, such that it will not move during the cutting and grinding steps, but the friction is not so excessive that distortion of the natural shape of the core would result. The core is secured such that the parting line of the core is roughly parallel to the top of the holder. The diameter of the core is measured 90 degrees to this orientation prior to securing. A measurement is also made from the bottom of the holder to the top of the core to provide a reference point for future calculations. A rough cut is made slightly above the exposed geometric center of the core using a band saw or other appropriate cutting tool, making sure that the core does not move in the holder during this step. The remainder of the core, still in the holder, is secured to the base plate of a surface grinding machine. The exposed ‘rough’ surface is ground to a smooth, flat surface, revealing the geometric center of the core, which can be verified by measuring the height from the bottom of the holder to the exposed surface of the core, making sure that exactly half of the original height of the core, as measured above, has been removed to within ±0.004 inches. Leaving the core in the holder, the center of the core is found with a center square and carefully marked and the hardness is measured at the center mark according to ASTM D-2240. Additional hardness measurements at any distance from the center of the core can then be made by drawing a line radially outward from the center mark, and measuring the hardness at any given distance along the line, typically in 2 mm increments from the center. The hardness at a particular distance from the center should be measured along at least two, preferably four, radial arms located 180° apart, or 90° apart, respectively, and then averaged. All hardness measurements performed on a plane passing through the geometric center are performed while the core is still in the holder and without having disturbed its orientation, such that the test surface is constantly parallel to the bottom of the holder, and thus also parallel to the properly aligned foot of the durometer.

Hardness points should only be measured once at any particular geometric location.

It should be understood that there is a fundamental difference between “material hardness” and “hardness as measured directly on a golf ball.” For purposes of the present disclosure, material hardness is measured according to ASTM D2240 and generally involves measuring the hardness of a flat “slab” or “button” formed of the material. Hardness as measured directly on a golf ball (or other spherical surface) typically results in a different hardness value. This difference in hardness values is due to several factors including, but not limited to, ball construction (i.e., core type, number of core and/or cover layers, etc.), ball (or sphere) diameter, and the material composition of adjacent layers. It should also be understood that the two measurement techniques are not linearly related and, therefore, one hardness value cannot easily be correlated to the other.

When numerical lower limits and numerical upper limits are set forth herein, it is contemplated that any combination of these values may be used.

All patents, publications, test procedures, and other references cited herein, including priority documents, are fully incorporated by reference to the extent such disclosure is not inconsistent with this invention and for all jurisdictions in which such incorporation is permitted.

While the illustrative embodiments of the invention have been described with particularity, it will be understood that various other modifications will be apparent to and can be readily made by those of ordinary skill in the art without departing from the spirit and scope of the invention. Accordingly, it is not intended that the scope of the claims appended hereto be limited to the examples and descriptions set forth herein, but rather that the claims be construed as encompassing all of the features of patentable novelty which reside in the present invention, including all features which would be treated as equivalents thereof by those of ordinary skill in the art to which the invention pertains. 

What is claimed is:
 1. A golf ball comprising a core and a cover, wherein the core consists of: a solid inner core layer formed from a plasticized thermoplastic composition TP_(p) and having a diameter of 1.10 inch or less and a center Shore C hardness (H_(center)) of 15 or less, an intermediate core layer, and an outer core layer formed from at least one of a thermoset rubber composition and a thermoplastic composition TP and having a thickness of 0.40 inches or greater and an outer surface Shore C hardness (H_(outer surface)) of 70 or greater, wherein H_(outer surface)>H_(center), and H_(outer surface)−H_(center)≧55.
 2. The golf ball of claim 1, wherein H_(outer surface)−H_(center)≧65.
 3. The golf ball of claim 1, wherein H_(outer surface)−H_(center)≧75.
 4. The golf ball of claim 1, wherein H_(outer surface)−H_(center)≧80.
 5. The golf ball of claim 1, wherein H_(outer surface)−H_(center)≧60.
 6. The golf ball of claim 1, wherein the inner core layer has an inner core interface Shore C hardness H_(inner core interface) such that −5≦H_(inner core interface)−H_(center)≦5.
 7. The golf ball of claim 1, wherein the outer core layer has an outer core interface Shore C hardness H_(outer core interface) such that H_(outer core interface)−H_(inner core interface)≦H_(outer surface)−H_(center).
 8. The golf ball of claim 1, wherein the outer core layer has an outer core interface Shore C hardness H_(outer core interface) such that H_(outer core interface)−H_(inner core interface)>H_(outer surface)−H_(center).
 9. The golf ball of claim 1, wherein the plasticized thermoplastic composition TP_(p) comprises: a) an acid copolymer of ethylene and an α,β-unsaturated carboxylic acid, optionally including a softening monomer selected from the group consisting of alkyl acrylates; methacrylates; fatty acids; and fatty acid salts; b) a plasticizer; and c) a cation source present in an amount sufficient to neutralize from about 0 to about 100% of all acid groups present in the composition.
 10. The golf ball of claim 9, wherein the plasticized thermoplastic composition TP_(p) further comprises a non-acid polymer selected from the group consisting of polyolefins, polyamides, polyesters, polyethers, polyurethanes, metallocene-catalyzed polymers, single-site catalyst polymerized polymers, ethylene propylene rubber, ethylene propylene diene rubber, styrenic block copolymer rubbers, alkyl acrylate rubbers, and functionalized derivatives thereof.
 11. The golf ball of claim 10, wherein the acid copolymer of ethylene and an α,β-unsaturated carboxylic acid does not include a softening monomer, and wherein the acid is selected from acrylic acid and methacrylic acid and is present in the acid copolymer in an amount of from about 15 to about 30 weight %, based on the total weight of the acid copolymer.
 12. The golf ball of claim 10, wherein the non-acid polymer is an alkyl acrylate rubber selected from ethylene-alkyl acrylates and ethylene-alkyl methacrylates and is present in an amount of greater than 50 wt. %, based on the combined weight of the acid copolymer and the non-acid polymer.
 13. The golf ball of claim 12, wherein the ethylene-alkyl acrylate is ethylene-n-butyl acrylate, wherein the n-butyl-acrylate is present in an amount of 20 wt. % or greater, based on the total weight of the non-acid polymer composition.
 14. The golf ball of claim 1, wherein the outer core layer comprises at least one of natural rubber, polybutadiene, polyisoprene, ethylene propylene rubber (EPR), ethylene-propylene-diene rubber (EPDM), styrene-butadiene rubber, butyl rubber, halobutyl rubber, polyurethane, polyurea, acrylonitrile butadiene rubber, polychloroprene, alkyl acrylate rubber, chlorinated isoprene rubber, acrylonitrile chlorinated isoprene rubber, polyalkenamer, phenol formaldehyde, melamine formaldehyde, polyepoxide, polysiloxane, polyester, alkyd, polyisocyanurate, polycyanurate, polyacrylate, and combinations thereof.
 15. The golf ball of claim 1, wherein the outer core layer comprises at least one of ionomers; highly neutralized ionomers; non-ionomeric acid polymers; polyurethanes, polyureas, and polyurethane-polyurea hybrids; polyester-based thermoplastic elastomers; polyamides, copolymers of ionomer and polyamide, polyamide-ethers, and polyamide-esters; ethylene-based homopolymers and copolymers; propylene-based homopolymers and copolymers; triblock copolymers based on styrene and ethylene/butylene; derivatives thereof that are compatibilized with at least one grafted or copolymerized functional group; and combinations thereof.
 16. The golf ball of claim 1, wherein the intermediate core layer comprises at least one of ionomers; highly neutralized ionomers; non-ionomeric acid polymers; polyurethanes, polyureas, and polyurethane-polyurea hybrids; polyester-based thermoplastic elastomers; polyamides, copolymers of ionomer and polyamide, polyamide-ethers, and polyamide-esters; ethylene-based homopolymers and copolymers; propylene-based homopolymers and copolymers; triblock copolymers based on styrene and ethylene/butylene; derivatives thereof that are compatibilized with at least one grafted or copolymerized functional group; and combinations thereof.
 17. The golf ball of claim 1, comprising an intermediate core layer formed from at least one of natural rubber, polybutadiene, polyisoprene, ethylene propylene rubber (EPR), ethylene-propylene-diene rubber (EPDM), styrene-butadiene rubber, butyl rubber, halobutyl rubber, polyurethane, polyurea, acrylonitrile butadiene rubber, polychloroprene, alkyl acrylate rubber, chlorinated isoprene rubber, acrylonitrile chlorinated isoprene rubber, polyalkenamer, phenol formaldehyde, melamine formaldehyde, polyepoxide, polysiloxane, polyester, alkyd, polyisocyanurate, polycyanurate, polyacrylate, and combinations thereof.
 18. The golf ball of claim 1, the outer core layer has an outer surface Shore C hardness (H_(outer surface)) of 85 or greater, and wherein H_(outer surface)>H_(center), and H_(outer surface)−H_(center)≧70.
 19. The golf ball of claim 1, further comprising an intermediate layer disposed between the outer core layer and the cover. 